I assume she has not elected corporate taxation for the LLC.
this is a summary overview. It would be best for her to consult with a tax pro to optimize taxation. We don't know enough to say whether her consulting is an SSTB that could limit the QBI deduction (form 8995).
Consulting SSTB is defined in REG 1.199A-5(b)(2)(vii) - see below. There are other categories, and she may fall into one of them.
the benefit of having QBI income is that it MAY qualify for a deduction against taxable income. an SSTB has more limitations than a non SSTB business. there are many rules that can limit the deduction.
however, if taxable income is low enough being an SSTB doesn't matter except in the case where she was an employee in the last 3 years for a business to which she now provides consulting services. REG 1.199-A-5(d)(3)
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see this link for some additional details on SSTB and taxable income limit
https://ttlc.intuit.com/turbotax-support/en-us/help-article/business-taxes/business-
sstb/L01V9UEkQ_US_en_US
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former employee rules. if treated as a (former) employee she is not entitled to the QBI deduction.
(3) Presumption that former employees are still employees—(i) Presumption. Solely for purposes of section 199A(d)(1)(B) and paragraph (d)(1) of this section, an individual that was properly treated as an employee for Federal employment tax purposes by the person to which he or she provided services and who is subsequently treated as other than an employee by such person with regard to the provision of substantially the same services directly or indirectly to the person (or a related person), is presumed, for three years after ceasing to be treated as an employee for Federal employment tax purposes, to be in the trade or business of performing services as an employee with regard to such services. As provided in paragraph (d)(3)(ii) of this section, this presumption may be rebutted upon a showing by the individual that, under Federal tax law, regulations, and principles (including common-law employee classification rules), the individual is performing services in a capacity other than as an employee. This presumption applies regardless of whether the individual provides services directly or indirectly through an entity or entities.
(ii) Rebuttal of presumption. Upon notice from the IRS, an individual rebuts the presumption in paragraph (d)(3)(i) of this section by providing records, such as contracts or partnership agreements, that provide sufficient evidence to corroborate the individual's status as a non-employee.
(iii) Examples. The following examples illustrate the provision of paragraph (d)(3) of this section. Unless otherwise provided, the individual in each example has taxable income in excess of the threshold amount.
(A) Example 1. A is employed by PRS, a partnership for Federal tax purposes, as a fulltime employee and is treated as such for Federal employment tax purposes. A quits his job for PRS and enters into a contract with PRS under which A provides substantially the same services that A previously provided to PRS in A's capacity as an employee. Because A was treated as an employee for services he provided to PRS, and now is no longer treated as an employee with regard to such services, A is presumed (solely for purposes of section 199A(d)(1)(B) and paragraphs (a)(3) and (d) of this section) to be in the trade or business of performing services as an employee with regard to his services performed for PRS. Unless the presumption is rebutted with a showing that, under Federal tax law, regulations, and principles (including the common-law employee classification rules), A is not an employee, any amounts paid by PRS to A with respect to such services will not be QBI for purposes of section 199A. The presumption would apply even if, instead of contracting directly with PRS, A formed a disregarded entity, or a passthrough entity, and the entity entered into the contract with PRS.
(B) Example 2. C is an attorney employed as an associate in a law firm (Law Firm 1) and was treated as such for Federal employment tax purposes. C and the other associates in Law Firm 1 have taxable income below the threshold amount. Law Firm 1 terminates its employment relationship with C and its other associates. C and the other former associates form a new partnership, Law Firm 2, which contracts to perform legal services for Law Firm 1. Therefore, in form, C is now a partner in Law Firm 2 which earns income from providing legal services to Law Firm 1. C continues to provide substantially the same legal services to Law Firm 1 and its clients. Because C was previously treated as an employee for services she provided to Law Firm 1, and now is no longer treated as an employee with regard to such services, C is presumed (solely for purposes of section 199A(d)(1)(B) and paragraphs (a)(3) and (d) of this section) to be in the trade or business of performing services as an employee with respect to the services C provides to Law Firm 1 indirectly through Law Firm 2. Unless the presumption is rebutted with a showing that, under Federal tax law, regulations, and principles (including common-law employee classification rules), C is not an employee, C's distributive share of Law Firm 2 income (including any guaranteed payments) will not be QBI for purposes of section 199A. The results in this example would not change if, instead of contracting with Law Firm 1, Law Firm 2 was instead admitted as a partner in Law Firm 1.
(C) Example 3. E is an engineer employed as a senior project engineer in an engineering firm, Engineering Firm. Engineering Firm is a partnership for Federal tax purposes and structured such that after 10 years, senior project engineers are considered for partner if certain career milestones are met. After 10 years, E meets those career milestones and is admitted as a partner in Engineering Firm. As a partner in Engineering Firm, E shares in the net profits of Engineering Firm, and also otherwise satisfies the requirements under Federal tax law, regulations, and principles (including common-law employee classification rules) to be respected as a partner. E is presumed (solely for purposes of section 199A(d)(1)(B) and paragraphs (a)(3) and (d) of this section) to be in the trade or business of performing services as an employee with respect to the services E provides to Engineering Firm. However, E is able to rebut the presumption by showing that E became a partner in Engineering Firm as a career milestone, shares in the overall net profits in Engineering Firm, and otherwise satisfies the requirements under Federal tax law, regulations, and principles (including common-law employee classification rules) to be respected as a partner.
(D) Example 4. F is a financial advisor employed by a financial advisory firm, Advisory Firm, a partnership for Federal tax purposes, as a fulltime employee and is treated as such for Federal employment tax purposes. F has taxable income below the threshold amount. Advisory Firm is a partnership and offers F the opportunity to be admitted as a partner. F elects to be admitted as a partner to Advisory Firm and is admitted as a partner to Advisory Firm. As a partner in Advisory Firm, F shares in the net profits of Advisory Firm, is obligated to Advisory Firm in ways that F was not previously obligated as an employee, is no longer entitled to certain benefits available only to employees of Advisory Firm, and has materially modified his relationship with Advisory Firm. F's share of net profits is not subject to a floor or capped at a dollar amount. F is presumed (solely for purposes of section 199A(d)(1)(B) and paragraphs (a)(3) and (d) of this section) to be in the trade or business of performing services as an employee with respect to the services F provides to Advisory Firm. However, F is able to rebut the presumption by showing that F became a partner in Advisory Firm by sharing in the profits of Advisory Firm, materially modifying F's relationship with Advisory Firm, and otherwise satisfying the requirements under Federal tax law, regulations, and principles (including common-law employee classification rules) to be respected as a partner.
https://www.law.cornell.edu/cfr/text/26/1.199A-5
1.199A-5(b)(2)
(vii) Meaning of services performed in the field of consulting. For purposes of section 199A(d)(2) and paragraph (b)(1)(vi) of this section only, the performance of services in the field of consulting means the provision of professional advice and counsel to clients to assist the client in achieving goals and solving problems. Consulting includes providing advice and counsel regarding advocacy with the intention of influencing decisions made by a government or governmental agency and all attempts to influence legislators and other government officials on behalf of a client by lobbyists and other similar professionals performing services in their capacity as such. The performance of services in the field of consulting does not include the performance of services other than advice and counsel, such as sales (or economically similar services) or the provision of training and educational courses. For purposes of the preceding sentence, the determination of whether a person's services are sales or economically similar services will be based on all the facts and circumstances of that person's business. Such facts and circumstances include, for example, the manner in which the taxpayer is compensated for the services provided. Performance of services in the field of consulting does not include the performance of consulting services embedded in, or ancillary to, the sale of goods or performance of services on behalf of a trade or business that is otherwise not an SSTB (such as typical services provided by a building contractor) if there is no separate payment for the consulting services. Services within the fields of architecture and engineering are not treated as consulting services.
