Tenant Leaving Before Lease Expires, NEED HELP!

[Donny Random]

I have a tenant that informed me last month that she did not like the apartment and she wanted to move. I informed her that she would be responsible for the rent until we found a new tenant or until her lease expired. She and I have been working to find a new tenant the last month with no luck thus far.
She informed me this week that she has bought a house and that she is going to start moving this weekend.
I want to prepare myself for the possibility that she will not fulfill her lease agreement and will not continue paying the rent after she moves. What should I do in preparation for this?
What are my options? Help!