As she is my friend, I would avoid getting too strict with her. First, I wd ask her why she was not attending the rehearsals, it may be that she was stuck with something. Then, I wd talk to the rest of group, and tell them the reason. We wd continue with our practise, make a new routine which does not give much importance to my friend, so that it won't really matter if she participates or not. The key is to move on. We cannot be stuck, wasting our time trying to make her understand to do the routine. Its better to do it and prepare without her.