My question involves landlord-tenant law in the State of: Massachusetts

I'm a student currently studying abroad. I sublet my apartment to a girl I found on craigs list. I orginally quoted the price to her as being $700 dollars a month but I made sure to tell her that untill they got a third roommate the rent would be $925. She agreed to this without complaint. I loaned her $700 to cover the third roommates portion of the initial fees(first, last, deposit) on the condition that she would pay it back upon finding a third roommate.

I had things all worked out with my management company/landlord so that she would replace me on the lease until i got back so it may have been more of a lease than a sublet. I got everything signed and the girl was supposed to go down the next day and finish signing and paying the fees before she moved in.

Now fast forward to just a few weeks ago, I get a call from my father saying the landlord says the girl is unable to pay her rent and it is defaulting back to me. I email the girl and she tells me that there is a mistake and that she is paying the rest of what she owes this month. Two weeks later I find out she is moving out without informing me, I had my brother get pictures of her stuff to confirm she was indeed living there.

In an email to my father she cites her reason for moving as the apartment being unfit for her to live in, but i gave her a thorough tour of the place not long before she moved in and she liked it. The landlord is after me because they say because she never paid all the fees she wan't under contract, but they let her move in. Also she cashed the check i loaned her and refuses to acknoledge my emails. What really gets me is that she intentionally mislead me, if she had just been honest I could have lined up another person to take her place.

Anyone have any advice or questions as to what I should do now?