SHe's a cute little mare!!! I don't see any reason at all why she wouldn't be able to do low level dressage for you. I know nothing baout hunters so won't go there! But dressage, yeah for sure, would love to see her moving. If you let her lose in a round yard/arena and she goes for a bit of a trot/canter around, does she sit back and take the weight on her hind legs or does she fall onto the forehand? When you're looking for something for dressage, ideally when they're 'free' they will naturally take the weight over thie hind quarters- makes your job a heck of a lot easier!!
Best of luck with her she's a lovely little mare, I really like her ;)