I'm going to threaten to charge for maid service because my roommate brushed a counter mess onto the floor for me to clean.
Why is that enough to threaten to charge your room mate?
It's necessary because I've told her before to not do that.
I understand why you're annoyed, because it's rude to throw a mess onto the floor and not clean it up yourself. I think you should have another discussion with your roommate about what is acceptable and what isn't.
But that could lead to me looking like the jerk in the split and much better for her to dish out $10 for something she should know better.
If you resort to threats than you could make your living situation with your roommate awkward. They will probably become upset and may not learn their lesson. You should try talking to them first and making it very clear that their behavior is not okay.