I had a similar situation involving a roommate who was using the basement as a shooting gallery for him and his junkie friends (many years ago). We asked him to leave. No go. We asked the landlord to intervene and her response was "its your problem, if you can't get it resolved I'll evict you all." I don't believe the landlord has any responsibility (or legal right) to evict just one person.
You have a lease? What does it say? What is the duration? Breaking a lease before the end of the lease period can be expensive and you could forfeit all your deposits.
Or do you mean "rental agreement"? If its a rental agreement its probably month-to-month. Have the landlord re-write a new agreement, leaving the problem child off. Then give her an ultimatum (in writing): move out or we move you out. If she doesn't get out, next time she leaves the house pack up all her shit and put it on the curb. Then get a keg and change the locks--wait for the fireworks to begin. Let me know if you choose this option so I can come over and watch.
In my case, we all just moved out and went our separate ways. The junkie died of an overdose less than a year later. Sad.