My uncle owns a single family home in DC. Ten years a go he let a friend with personal problems stay in his finished basement. Over the years this lady has allowed the space to become unlivable: from the roach infestation, to, the cats and their feces EVERYWHERE! How can he get her out?

She is a resident and has to be evicted according to the rules for DC. Have him check with the local housing court as to what these rules are.

By the way, this question is frequently asked. Had you browsed through the threads in this forum you would have found an answer.