I have clients who make money dog-walking, babysitting for children/disabled/elderly/even pets on an occasional basis, handyman work for individuals/one-time-type work, and other paying gigs for individuals, seldom for businesses, and very seldom over $600 for a person. So, no 1099s expected or received. The clients report their income, some keeping better records than others. I report all income. I might suggest better recordkeeping &/or depositing it in their bank for a better paper trail. But, if I have no suspicions, I prepare their returns.
Your client's work for a restaurant should've been on payroll or at least a 1099 for sporadic, casual labor. Urge her to talk with the restaurant this year. Explain to her what to say &/or print out some plain English explanations.