I have always thought that horses that want to be on their forehand are often trying to keep weight off their hocks. Has she been evaluated for soundness and can she use herself properly in flat work?
I think this is a bigger issue than a bit can solve.
I have a horse that fits your horse’s description and we have been through the wringer the past few years finding the right bit. He is a hunter so our options were limited and we wanted to keep him in a full cheek and not a Pelham. We finally settled on a Waterford full cheek for the show ring. At home for schooling, we use a figure eight and a cartwheel. Over the years, with lots of schooling and various exercises, he has gotten so much better with being heavy, but when he’s out doing a derby course and decides he’d like to try to pull to the high-option single oxer, it’s nice to have a bit that discourages that!
How thick is the current bit? Sometimes horses lean because the alternative (as in the bit resting quietly in mouth) is actually less comfortable than leaning. This is doubly true if the harsher bit (e.g. twist) hits their palate in the wrong way.