What should I do my friend is in love with our Language Arts Teacher?

Well, he's 25 and she's 13. She thought he was boring until we saw that he had 2 tattoos. It was a teacher-student basketball game and he was playing.(that is how we noticed) Now she's obsessed with him she thinks about him all the time asks questions like "I wonder what he does after school...." She has openly told him that she loved him he has just been ignoring her. Me and my friend we have this special spot were we stand after school. He knows we stand there and yesterday he was standing there when we got out of homeroom. Of course she said "um lets go wait for our parents somewhere else..." He also was texting someone when we were walking by and she just shouted "Mr. - I THINK YOUR Y!" and she ran off pulling me behind her. I thought it was just a crush but I know its an obsesssion. She has little fantasies about him. It is creepy. She is not the only girl who likes him but she is the only girl who has taken it this far. I'm not sure on how I can help her.