Remember, they're a little more flexable (and headstrong) when they're younger, so it depends. But you might have a nice little mid-level eventer there. Don't rush training, though. That's the worst thing you could do. Jumping is particularly hard on their legs, and when they're growing, you can cripple them permanently.
Once you have the basics down - the walk, trot, canter and halt (halting is important
. I owned a mare who wouldn't stop at 11 years because she'd never been trained properly, and she was a Thoroughbred. I was younger then, and finally sold her. So sad, because I loved her - but it got to be dangerous after the third spill.
) - light dressage training might be nice. It'll teach her to accept you, follow your leads and trust you. That way, as you work over cavelettis (pardon my spelling, if it is incorrect), then jumps, she will know that it is safe. Feeling nervous, horses can:
1. Refusing to jump
2. Jump to high
3. Skirt around
Remember, never punish a horse because it won't jump. Mares especially are moody, and making them do something they're scared to do may end up doing more harm than good.
Sorry that I went off on a rant.
I think she'll make a great horse.