A separate account for your wife under your existing one-participant 401(k) plan (a misnomer since it allows both you and your spouse to participate) is required. Your wife does not have to be an owner of the company to participate in the 401(k) but she must meet the eligibility requirements that you established in the plan agreement. As an employee and not an owner, the amount available for her to electively contribute to the 401(k) will be determined by her available compensation from her pay (after deducting income taxes and FICA taxes), subject to the individual elective contribution limit for the year. Presumably the employer contribution is simply a profit-sharing contribution rather than a matching contribution, so the amount of the employer contribution will also be subject to the same base employer contribution percentage (up to 25%) as is used to compute the employer contribution for yourself.
https://www.irs.gov/retirement-plans/one-participant-401k-plans
https://www.irs.gov/pub/irs-pdf/p560.pdf
