OP, I recognise your username, so am going to approach this with a little knowledge of your previous posts. If that's not okay, I'll happily also report my post to have it removed if you'd prefer.
You've been through a huge ordeal, a lengthy process and it sounds like you've made huge progress to get where you are. Well done for that. I completely understand why you have been offered a school place for your child(ren) and agree that your circumstances should absolutely qualify for some sort of respite in this way if needed.
However, from what I remember, this past time has likely also been very traumatic for your children, and it is worrying the way you think your daughter might react to it (fwiw, my children were both offered places in school, but we had to weigh up the benefits with the lack of consistency and the 'unknown', so understand the concern) With you saying she's also in her own support group, it sounds like she's working hard on trying to move forward too, but I'd be worried about setting her back. Can whoever runs her support group / therapy give a bit of advice, a bit of feedback as to where they think she is and what she could cope with right now?
Honestly, if it were me, I would agree with trying to find some alternative place for her to be on your therapy days, but would do everything I could to make that be with a person and in an environment that she is comfortable and secure in. (Is there someone she trusts at school, who could differ a bit from the generic plan for in-school kids and take her under the wing for the day?) What about their dad? I know he was heavily involved, can he arrange to have them/her on your therapy days?
It's a difficult decision to make, and it sounds like you are thinking through all the options and determined to make the right call for ALL of you. Like I say, it sounds like you've done really well to get to where you are at right now. Well done 