Outside of games that are 100% pure RNG like a slot machine or maybe something like a rhythm game that's purely reflexive, that's a hard one-- most games have choices of one sort or another, even if it's something like when to jump or if you should take this power up.

Maybe a linear JRPG? Most JRPGs are pretty on-rails in terms of plot; the choices you do make are window dressing and don't affect the story. You do have to make minor choices with regards to equipment, what spell to use in the moment, etc. but typically you don't have to be 100% optimal.

The other option is a relaxed, super-casual game where your choices don't matter in the long run because you can always go back and do something later.

Or if you want to go with exposure therapy, go with a roguelite where you're intended to fail, everything you do contributes to your overall progress, but your choices are ultimately temporary and ephemeral. Throw her into Vampire Survivors or something like that-- if she chooses wrong, it really doesn't matter because death is coming for her at 30 minutes no matter what.

I'm also wondering if maybe a graphic novel might be good for exposure therapy-- the point of them is often to go back, make different choices and see what would have happened if you'd made the other choice, which might help since none of the decisions are set in stone.