They did a credit check on her because she was in a position that dealt with money. Theoretically someone with good credit would be less likely to find ways to dip into the till than someone with bad.
The thing that irks me is that every time someone runs a credit check on you it lowers your score.
That's a half-truth.
I went postal a few years back when I saw something like 10 'inquiries' from Home Depot among others in a short period.
(Disclaimer - not an expert in this field) but if you are currently holding credit with a merchant you are not penalized on the inquiry. That is is not to be confused with 'new' credit requests which do attach flags.