What should I do about a former employee refusing to return company property?

A former employee that left under amiable terms is giving me excuses why she won’t turn in the main building magnet key. First she told me it was the one I gave to another employee, which I had a clear enough memory to know that wasn’t the case and confirmed such with the other employee. Let me give you two points about my interaction with this employee to give you a feel of what it was like. She always had this cavalier “I will do what I please attitude”, half of her responsibilities she blew off, giving me excuse after excuse, but what she did she did well. The day she left, she took the liberty to go into her own employee file and shred about half the file.
I have a verbal agreement to pay her a small commission on some work she reeled in that hasn’t been paid yet. So here’s the dilemma for me, here I am prepared to follow through on my obligation to her, and bit my tongue on various things to make sure this was an amiable divide, but she is giving me flippant “sorry I lost the key magnet”, which will cost me $25. It’s not outside reason that she could have made copies to the other keys and still has access to the office, which will also cost me a lock changing fee if I consider this a risk. What should I do?????