Yes, check for pain or any tight muscles and saddle fit, etc.
Then consider this. Maybe she's found a loophole in everyone's plan to ride her. She rears or bulks.. and what happens? Oh they get off, or maybe they freeze themselves and do nothing, or maybe they're scared of her.
I'm not sure exactly what this loophole is, but she has found it.
Have you dealt with a rearer before? Baulking is a little bit easier to work with but can escalate as well... I've dealt with the wall-scraper. That's never fun.
Fix that hole or find someone else to.
"Strength is the ability to use a muscle without tension"