If she is lax in getting her expenses turned in, then you are at the minimum paying the interest accrued on the credit card due to those trips, possibly late fees too. I'm sure she's not turning in the interest or late fees on the expense reports, the company probably wouldn't pay for that.
At the very least I would do what NOPkins suggested, call and speak to someone over accounting and ask for a copy of their travel policy, inquire about why she is expected to use her credit card. This just doesn't seem right to me....how big is the company she works for?
