I, too, have been in that situation, albeit a long time ago. Lies were told about me and suddenly i was cast out of my friendship group. Even my best friend turned her back on me. Luckily for me it was the end of high school and that meant I could make a clean break. It hurt like hell, though.
It happened again later with another person, who suddenly avoided me and pretended he wasn't in the country, ignored texts and never told me why. I never spoke to him again and became really depressed.
I agree with Suzanne about asking questions, but if the situation is such that she won't even acknowledge you, there isn't much you can do. In that case, I would focus on doing activities that make you happy. Delve into your special interest or indulge in favourite TV shows/video games or whatever you do to distract yourself for a while. Lay your favourite sport if that's your thing. If you're comfortable with going new places you could try out a new hobby or club that has interested you.
Change is hard for us, and change forced upon you in the cruelest way is the worst. So doing your favourite thing for a while, i.e. being kind to yourself, may make the transition a little easier to ride through.
By the way, I've had several phases of my life with different friends, then have moved on to a new place and met different people. A bit like living several lives over the course of one lifetime. Over time I learnt to not mourn the loss of old friends, but to look back and simply appreciate having had those friendships at all. Being grateful I had those experiences. Without those friendships and those experiences I wouldn't be where I am today.