So I hauled the monster pony home for a lesson today which was helpful. It wasn't fun driving an hour up to get her and an hour back down to have a lesson, then up and back again. But at least it was worth it. JF helped with Jetta's heaviness on the bit.
Basically, here is what she told me. When Jetta leans on the bit and rushes, hold her (don't pull) and close your leg to send her forward. If she doesn't lighten on your hands, then give her a little bump to let her know that you're serious. Don't do any upward or downward transitions until she is light on her forehand and in your hands. In the canter (where she's super heavy) hold her and sit really deep in the saddle and think of picking up her forehand, almost thinking "backward" like you are asking to back up. As soon as you get the feel you're looking for, ask to transition down. If she doesn't listen, bump her again. Always insist that she does what you want immediately. When you ask to collect at the walk, she can't lean on you for three strides until she lightens, she has to be soft immediately. Same with upward transitions, when you go from trot to canter, make sure she transitions when you ask, not later, if she fast trots too much, slow down and start again.
Another option if she's leaning and not listening to your cues (body then seat then hands) reach down and bend her quickly until she's light and then immediately go off again, making sure she's using her whole body. If she goes too fast and doesn't slow down, instead curling behind the vertical, bump on one side or the other to get her uncurled.
Jetta was ok. She wasn't a star pupil or anything. She was pretty sticky when we were warming up with our shoulder-ins which was a little disappointing cause they were so good! Overall it was a beneficial lesson. A lot of the tips I was already using, so basically it was a refresher and it helped show me that Jetta's not a baby any more so she needs to start doing things like a grown-up ;)
I also need to work on her being more responsive to my leg at the walk and turn (she's already super sensitive at the trot and canter) because she can be a little non-responsive. I think our next ride is just going to be ground work. After our lesson, I rode one of JF's horses in exchange for my lesson. He was such as cutey! She bought him as a resale prospect - he's a little 14.1hh quarter horse. He seems so tiny compared to Jetta! He's super sensitive but I like him. I felt like my legs couldn't touch him he was so short. There was a moment where he was like "OMG where did those legs come from?!" But he was pretty good. It makes me want a young western prospect to train for reining and trail. Sigh.. Maybe someday. Today has given me a lot of motivation to keep working with Jetta so I can't wait to ride her again soon!