Yes, beauty salon owners that are self-employed (meaning their business entity is not set up as a C Corporation) are eligible for the Qualified Business Deduction.
And, yes, if your sister had any Schedule C business income during 2018 - even if the business closed during the year -- she would be eligible to receive the Qualified Business Income deduction on her 1040 return as long as her Schedule C business activity is reported, plus that she has taxable income on her tax return (taxable income is one of the variables in the deduction calculation).
Here is more information on the Qualified Business Income Deduction:
https://ttlc.intuit.com/replies/7019998
