This isn't so much a legal question as a technical question. It's based on what background checking service they use.

Background checks are typically limited depending on what the client is willing to pay and how long they want to wait.

Even today there are many many many counties and small towns that don't have all records online or have old databases that don't interface with many national or state level systems.

Many employers and landlords limit the years they go back on searches. They also limit what types of criminal background to search.

If the employer is in sales they are likely to care most about crimes of moral turpitude (stealing mostly). An employer that has drivers is going to be most concerned with stealing but particularly dwi/dui. However, they may only care about it being within X years in the past. Sometimes this is dictated by client contracts. The more stringent the contracts/clients the more stringent the check. It's the same with housing and apt communities. Their worst fear? A predator, sex offender, domestic disturbances, property destruction/vandalism crimes.

***My answer? Tell her not to even mention it on the application.***

Lying on the application is not illegal either. It's just a right for them to not approve or hire you. The whole thing is rather silly. B/c 99% of the time they will reject you just by your admission (which is what they hope for with this tactic - a shortcut to rejecting "bad apples"). Since it's not illegal and only a reason for them to throw away your application why mention it at all?

It's probably >97-99% of the time it won't come back on background checks but *IF* she admits it up front on the application there is a high likelihood of immediate rejection.

Tell her not to mention it. It didn't happen.

Even if you have something a bit worse you do not ever ever ever admit criminal charges, arrests, tickets, etc on ANY job or housing application. I don't give a crap what some ridiculous ethical job hunting website or scare tactic legal site tries to tell you.

DO NOT EVER DO IT WITH EXCEPTION TO THE FOLLOWING:
Job applications with the CIA, FBI, NSA, or any other 3-letter agency or other govt institution. The other one would be an adoption which all require a complete nationwide FBI background check that takes up to a month (I've been through one doing my older sons adoption). First of all those are more likely to be considered valid legal documents and even more likely to try to prosecute you. However, the other reason is b/c those places *will* find it (if there is anything) and you will be done anyway.

I don't care what anyone tells you, a regular job or housing application is not a valid prosecutable legal document. It's a scare tactic for the most part to get you to admit something upfront. I repeat, lying on applications to regular jobs or housing is *not* illegal. I don't care what it says on the application (with exception to what I mentioned above). As much as the employer would like you to think it's a form of fraud it is not (it may be a form of "lying" but it is *not* legally "fraud"). Why? It's not a valid legal document and it isn't governed under any statute.