While everyone is saying this girl is crying out for help, that may not be the case. Do you know what her family is like? Does her mother wear pants regularly? If that’s the case, and the parents don’t care if she wears pants, then you have a big problem. Parents must reinforce at home what is taught in school.
I think there needs to be a meeting with the parents, and some things might be said which they find unpleasant. If the school is BY type, and the parents don’t care if she dresses in pants, they should be asked, “Why are you sending her here?” Make it clear that the school has certain standards that she must adhere to. Explain that if the mother wears pants, the girl will only be conflicted as to what is right. It may be that the school is not the right place for her.
If the parents are not aware of what she’s doing, and want her to shape up, then just discuss with them what is going on. Ask for their assistance. Maybe something is going on in her life which is causing her to lash out? Parents and teachers need to work together.
One other point which occurred to me as I was typing this is her other teachers. I assume you’re not the only teacher she has? Have you spoken to the other teachers to find out if she’s acting the same way with them? If it’s only with you, then you might need to talk with the principal and try and figure out why that may be.