I would try really hard to find a sport completely different from the ones her sisters play. Do you have lacrosse near you?
I also wouldn't give up on basketball. If she can handle the ball, hit an open shot, and play great defense she will go far. Shooting and defense are almost entirely practice and effort based, she can do that and any coach would love a pass first, good open shooter who also plays defense.
As someone who played high level tennis until college, do not do that. It's an incredibly lonely sport and when you lose, its 100% on you. Also if she's 11 and hasn't already played a ton, it's impossible to catch up without some major growth or athletic spurt.