Not the same, but -
I moved out of my first apt on or just before Dec 31, paid through the end of the year. This was a 1 bedroom $295 a month junker. Late Spring came around, and I got a bill for $175 for a "grease spot" on the living room carpet. I can only assume they used that term because I worked next door to my apt, as a mechanic.
I had pictures from move-out day. I told them to prove it; they said they had pictures. I filled them in with the fact that I had dated pictures from move out day and to prove I did it ( I did not ).
They called me and very we're-better-than-youish said, "Do you really think WE would waste our time on YOU or $175 if we weren't sure we were right?" I faxed them a letter with my (dad's) lawyer's number, and I never heard back from them.
Sorry for the long reply, but the point is, SOME of these bastards will try anything to get some extra vacation spending cash. In your specific case, I would make them press harder. You should have access to all the steps you can take to fight the collection appearing on her credit pull. But, don't do anything stupid like looking her up at work; as you likely know, people get canned for that.