One of the biggest delusions/urban legends that seems to be held by a whole lot of people is that there is some sort of universal data base of everybody's employment record out there somewhere. And that potential employers can check this.
I cannot count the calls we received at Labor in the course of a day, requests that we "...send me a copy of my work history, you know, everywhere I've ever worked, and the dates I worked there."
If you aren't keeping up with this, nobody is keeping up with it. Unemployment system keeps people's wage records by ss# and by quarter, a quarter rotates off each time one passes, so this is about 18 months back and NO ONE, no one except the individual or an affected employer can get any information about it. (And this only comes up when a claim is filed, you can't just call and check on it without a claim.)
Likewise social security, which keeps up with an individual's work for covered employers by year, not easy to obtain, and certainly not for the prospective employer.
A criminal background check will of course only bring up anything you have been actually charged with in the legal system. They would not have done this without your being aware of it.
So it sounds as though the only place this could be coming up is in the person's employment records with the individual company when they request a reference. What they have is that she was discharged for theft. She was. Even if there were a law, which there isn't, would they be supposed to lie? Some companies will only give out the dates a person worked there, and whether or not the person is eligible for re-hire, but this is not required legally.
The only thing she could possibly do is explain to the prospective employer what it is going to say beforehand, and try to cover what it says with an explanation pro-actively. She would, of course, want to point out to them that she had two years without a complaint or problem with this company.