Terra.. I have to agree with Chojin, however, Ziggy's opinion is also a good one... if you could get away with it!.
Be proud of yourself that you stood up to enforce the rules you set in the beginning. If the girl has any sense at all she will see that you are only trying to do what's best for her daughter. Unfortunately, like Chojin point out, most people will continue to take advantage of you if you let them.
Stick to your guns on this one. Chances are if she does move out she will be begging to come back soon enough!