A few points:
Did you actually see the ChexSystems report, or was she just declined for a deposit account?
If she was just declined for a deposit account by qualifile, then it could simply be that she has a security freeze on chexsystems, or some other reason other than a derogatory on her report.
If you saw the actual report, I guess it depends on the situation.
There's no way I'd want a teller with multiple reports of fraud, acct abuse, or kiting, on her report. OTOH, I wouldn't be overly worried about a teller who say had a paid NSF closure from 4 years ago, with no other derogs.
Also, does your FI have a policy to address this? If your bank has a policy that chexsystems derogs=no hire, then well, there you have it. Otherwise, why are you even looking...
Are individuals who don't meet your banks underwriting standards for a credit card barred from being tellers?
Are individuals who don't meet your banks underwriting standards for a car loan barred from being tellers?
Are individuals who don't meet your banks underwriting standards for a mortgage barred from being tellers?
See where I'm going with this?