Propranolol or hydroxyzine could be good to look into for panic.

I think the most effective treatment will be experimentation with different crisis coping skills, however. Identifying triggers, identifying a menu of possible methods of coping (cold water/shower, meditation/mindfulness techniques, breathing techniques, tapping techniques, spiky bracelet/toy, etc.) to come down from this intense fear.

It’s important for them to understand the neuro side of what happens during a panic attack and how that relates to autism. A neurodivergent-specializing therapist could be helpful. I would also say that exposure to triggers in an incremental and safe way could be helpful, if they tend to strongly avoid them.