I am a landlord renting a property to 2 roommates in Washington DC. One roommate decided to leave w/o notice. She only informed me that she intends to leave with no specific date or formal letter. She has now left. I have a 1yr lease with them, which ends in June 08 signed by both of the roommates. It shows the total amount due every month with no specifics of each responsibility. They usually pay ½ each. I am trying to rent the house (or find the guy another roommate). She has not paid her Dec 07 rent and said she won''t be paying anymore (she actually moved to Dallas). Until I rent this place, what legal right do I have? Can I sue her separately? What court do I file in? I don''t want the other roommate to move out leaving me with an empty house. But I want to hold her responsible for her portion. She claims that it''s my responsibility to “Mitigate Damage”. On top of that the roommates are not in speaking terms now. Is this a landlord/tenant issue or smalls claims issue? Rent is now late and she's not paying anymore. I want to take her/them to court.

This is a roommate/roommate issue. She is still responsible for the rent. Until another roommate can be found and replaced on the lease, she is responsible. He is also responsible for finding that roommate or coming up with the rent.
This has little to do with you until the rent is late - unless you WANT to be more involved.