My children have always been given the right to say no.
To a play date, a party invitation, a game at recess, whatever.
I don't expect them to play or be friends with everyone.
I DO expect them to be kind and compassionate and get along with everyone at school, or in any other social situation, to the best of their abilities.
You are right, in the real world we have no choice over who we work with, or live next to, but we DO have a choice over whom we socialize and form friendships with.
Also, try not to use the term bully lightly. A bully is someone who repeatedly and aggressively goes out of his/her way to target a specific child or group of children. Kids say and do "mean" things all the time, that's not the same as bullying. Especially among girls, they change their bffs like they change their socks. It's all part of growing up.
As far as resources? I think Girl Scouts, theatrical productions and team sports are all very empowering for girls. By age 10 or 11 boys become a huge distraction and source of competition among many girls. They should have lots of opportunities to work and play and compete without the boys around. They will form stronger bonds and be less likely to slip into mean girl drama later on.