I didn’t know I had autism until my 30s but…

Maybe have her slowly learn to practice mindfulness? I picked up some aspects of it around that age while doing martial arts. https://www.mindful.org/mindfulness-for-kids/

If she can learn to realize she is about to have a meltdown she can hopefully have a less intense experience with it. Think of that as turning down the volume before a commercial break interrupts a movie with way louder sound.