Instead of a child getting taken away by Social Services, would it be easy for me to have her stay with me?

Here is some more background... I was picking up my step daughter from school a couple weeks ago and her friend gave me a letter she wrote for me. It was telling me that her father touches her and she is scared to go home everyday. After I read the letter I was shocked. I have never dealt with anything like this before. I asked her if she has ever told anyone about this. She told me a couple years ago she told the principal of her school (who is still the principal now) and that some lady went to her house, but im guess it was unfounded because she is still living there. A little background on her, she is 12 years old, she has been held back in school, she gets in a lot of trouble and she also likes girls. I dunno if all that is signs that it is really happening or not. When I told her I was going to go to the principal she told me no and that she would run away and she told me she already told her dad that she told someone so he will get in trouble if he does it again. That makes me think she isnt being truthful. So I ended up going to the principal yesterday and gave him the letter she wrote me. He told me he was going to call Social Services immediately and they will hold her at the school till they arrive and she wouldnt be allowed to go with her dad if he came to get her. I He told me I did the right thing, but this is all I can think about. Her 6th grade graduation is tomorrow. my questions are, is she going to be able to go to her graduation? If this is founded and she is taken away, what are the chances of them letting her stay with me temporarily? Also, is it dangerous for me to get involved? I used to see the dad everyday picking up my step daughter and i need to protect my family. Also, her mom lives is Mexico and she never talks to her so she isnt in the picture. The child lives with her aunt and dad.. Any advice would be greatly appreciated. Thank you!