Since the one really wants to be on her own, I think you are making the right decision to separate them. I also think the sooner the better. They won't be able to remain together forever and the longer you wait to do it, the harder it will be. Yes, tell her teacher about it. The more information the teacher has the better. Good luck! I have a feeling she will be over it within a couple weeks.

Tracy
Mommy to Lindsey, Patrick and Brooke
Born 1-14-03 at 32weeks, 3 days and ^i^ twins Dylan 1-12-02 and Cole 1-21-02