Well, not actually lying, she just said before she had somewhere else to stay in two weeks ... but she'...
I am presenting the opposite point of view as yours, necessary to keep "takers" from essentially stealing from you, since you aren't familiar with using it. And by shaking you up it may jostle your present mindset into acting different and the sooner the better. If you are on this forum it is because you probably have problems preventing getting hurt.
Getting her out now is most essential I think. You don't need to wonder one more minute. You do not need to care about her welfare because she does not care about you. She will take whatever she can pry from any helpless person. She may be able to convince people she is sincere but it is an undetectably phony act.
I would not have waited for her to get there. I normally give people 15 minutes to respond. It is healthy for you and her to have respect for others' time.
Seems like she is a lying liar. With the allowance you already showed it is hard to change to a drastic approach, but it won't matter in the end. I would throw a screaming fit in attempt to scare her to get out NOW! She sees weakness in you as her opportunity to continue abusing you.
She's not emotionally humane in my mind and doesn't deserve consideration. Don't let her talk because she has no justification. You have no justification in letting her use you.
Your roommate has no respect - too arrogant or scared to ask and discuss it with you ahead of time, or to get the facts from the girl ahead of time. He didn't care about your possessions, your safety, or your refuge. He denies his subordinate position. I would intimidate him and read him the riot act. Tell him to get her out now, no excuses, or threaten him with losing his residence.
That is the only way I have found to deal with people who don't care about you. Get them out of your life. They will continue to use and hurt you and others until they learn. Guaranteed. Some people aren't capable of learning that.
Just threaten, scream, scare them, get other scary people to help you, etc. like your life depends on it because it does.