Sounds like she is working her butt of to make a little bit of money while going to school full time. I think not charging her rent would be alright as long as she continues what she is doing.
Now if she quits school and her jobs then yeah, charge her rent or boot her out.
I do like what MonkeyBiz's parents did for him too.
Money doesn't buy happiness?
Have you ever seen a sad person on a jet ski?