I'm with everyone else. She has definitely improved from the 2' to the 2'11. Whether it's the rider (which is a big part of it) or if it's her becoming more comfortable, she isn't rushing the jump as badly. She definitely has the scope and range to go higher, and she also has very nice knees.
On a note with the rider, I liked how she stayed with Bella, holding her gently to keep her from rushing the jump, but then sat quietly and had quiet hands over the fence. It is on of my biggest pet peeves when people yank on a horses mouth over the fence. It might just be me, but I would rather see a properly executed crest release than an improper automatic release any day of the week.
I've got a suggestion to help with rushing fences. I had a horse who rushed and one thing my trainer did to help with that was to place a group pole a stride out from the jump. Then, as she approaches, she sees the ground pole and has to think about where she is placing her feet instead of just rushing the fence blindly with her head up. It worked for me for that mare.