I take it most of you have never really dealt with landlord tenant laws, or you don't live in a major metro area.
You can't just change the locks on someone, or just kick them out, or use these stupid bully tactics. There are laws set to protect people from being unjustly removed from a dwelling, whether they are on the lease or not. Something does not have to in writing to be a legal contract - someone living at a residence is a legal, oral contract, and you accepting contributions from her is paper evidence that there is a legal, oral contract between you and her as a roommate.
Doing stupid, juvenille shit like changing locks is an easy way to get sued, and reamed for punitive damages. Courts don't take kindly to illegally evicting / locking people out. FFS she's also a female with 2 male roommates she would have a field day with you in court.
The more you describe how you're doing things the more it becomes very obvious you need to stop everything what you're doing, send her (and your landlord) a certified letter stating your intent to move on a certain date (with proper notice), and GTFO.