Fix It Friday
Today's submission comes from Whitney, who says that this mare is struggling to relax and be soft, especially at the lope.
Whenever I'm trying to address an issue like this, the first place I look is the equipment. The biggest thing that stands out to me is the curb cranked way back with either no curb chain, or one that is way too loose. This causes it to act like an elevator, which encourages the horse to lift the head, and brace against it using the underside of their neck. I assume the tie down has been put on to combat this head lifting, rather than just addressing the cause of the issue. The saddle also appears to be bearing down on the shoulders and withers, which can cause discomfort and further encourages the hollowing reflex you've already initiated with the bit.
The rider looks decently balanced in the saddle, if not a touch behind the motion. This is likely due to the described choppiness and stiffness, as it can be hard to sit correctly square when a horse is racing. The rider is also pulling down as well as across, which is the opposite of the motion you want to do with a curb.
Overall, I see a rider and horse that need to go back to basics. I usually recommend a full cheek French link snaffle or loose ring lozenge for horses going back to the beginning. Lots of time at the walk practicing bending and lateral work, then stepping up to the trot ONLY when the walk work is completely solid, etc etc. Best of luck to you both, she's a beautiful horse that would have a lot of innate athleticism once she's working properly.