Hi 
I understand the anguish here OP. I think most mothers would end up feeling like you do for exactly the same reasons.
But, hopefully to reassure you, it seems your DD has found a groove that works for her for the time being. When we go into fight/flight/freeze or fawn, regardless of whether we are neurodivergent or not, we do sometimes want to hide away & be on our own. Panic attacks are terrifying but they don’t harm us and she clearly has found her own way of dealing with these right now.
However, would it be helpful for her to speak more openly with her therapist? Probably! And it’s great that she has one to begin with yet it seems a shame to miss out on support he could provide by not talking with him openly/regularly. Ideally she should be able to access and receive proper therapy for the panic & SH (even mild SH). The triggers are important but her response is more important.
Could she improve her coping skills? Absolutely - but she would need to want to improve things for herself. And this is the rub because this is the part that a big question mark hangs over bc there is more she can do but does she want to? She probably just wants it all to go away in reality and to not have to deal with any of it.
Can you help? Yes. And I would perhaps begin by asking your daughter how comfortable she is with her therapist. Does he really “get” her? Ideally she should be valuing & benefitting from the support and it sounds dubious that this is the case.
If not, find new therapist who is relatable, specialises in anxiety and SH. Maybe someone with lived experience. Personally I find stories of people who have been through what I have, inspiring, reassuring, validating & helpful. So maybe curate some stories of ppl who have recovered for her to see that it’s possible.
Finally, we have to sometimes watch our young struggle a bit while they find their own way and that can be so hard. I’ve had it with my own too. Sometimes we need to watch as they hurt and wait for the invite instead of wading in and fixing things.
You will both find the way. I found asking cleverly worded questions useful. 