Q. I guess only real concern is is like how do I know my W-2s correct? How do I know that that information on the W-2 is correct and that she included her pay me in cash?
A. There is no way to do that, after the fact. You needed to do your own record keeping at the time, if she didn't give you a "pay stub"/receipt. For example, you got paid $10/hr for 10 hours work and received $80 cash. Receipt of your W-2 should account for the missing $20 in boxes 2,4,6, & 17 (and sometimes box 19).
https://www.irs.gov/pub/irs-pdf/fw2.pdf
