She looks like a great all around pony. I would try hunter/jumper, trail riding, and I bet she would be good at gymkhana. It all depends on if she likes to do it, that's the main idea. Because if she doesn't enjoy what she's doing she isn't going to pour her heart into it.
From the pictures. I would say huntseat or just english riding. No saddleseat, you would never do very well, since this horse is a stock horse. I'd have to see a video of you riding her to say for sure.