At the Villages of Fairview (75/Stacy) in the area behind the mall there is a place called "The Beach" where there is sand volleyball. There is also a splashground, and there are often some older kids at both.
Cosmic Jump off of northbound 75 in Allen (I think off ElDorado) is fun anytime, but they also have Jr High and Sr. High jump times when she'd be able to meet other kids her age. Jump Town in Far North Dallas is similar. Check Groupon for deals at these places, as they can be pricey.
If you belong to a church, their youth activities would be a good way for her to meet others. If you have a community pool, that may also be a place to meet kids.