track or cross country are always great fallbacks that take most people and would do great to work with endurance and/or burst speed.

Surprisingly, keeper skills in soccer and libero and blocking skills in volleyball overlap a lot (depending on her height).

I went through a similar deal when I was younger with basketball. I had only ever played PF all growing up because I was a bigger kid, until at age 14 everyone else's height caught up, and playing a 5'9 PF was no longer helpful against 6'+ guys. One coach tried to move me to SF, trouble is I only really knew how to post up and rebound, I never needed to pass or shoot much, and couldn't make the move.
Made the switch to volleyball, hoping my rebounding skills translated to blocking well enough since I could jump pretty good, and it did. I was never a good hitter, and I later figured out I was better at digging and receiving at my height and became a decent libero by senior year (although I prided myself on being able to match blocking height with one of our middle hitters who was 7 inches taller than me).

If she was a good keeper, there are plenty of other things she can do to help her skills if she can't play keeper at the moment, and she may end up finding something else that her training could be beneficial for that she may like more.