What seems to be an entire lifetime ago Riley was in a very similar siutation to Zoe.
She was on target with her cognative skills and her biggest area of delay was motor skills. I had the exact same fears you do. We fought hard to have her in a program like Langan is in. Typical kiddo's with the SN kids. That way there is plenty of typical interaction as well as the therapies and IEP goals.
Sine the only program around here is out of our county we weren't able to get the county to pay for her to go and paying out of pocket was unrealistic so we conceeded and allowed her to go to the developmental preschool.
The program was ok, she turned out to be a leader in the classroom, which was great for her self esteem. She was not the highest functioning kid, but not the lowest either. There was another little boy there who had CP, but was right on target for his age. Riley and this guy became buddies, my problem came in when Riley started wanting to crawl all the time, like he did. Had I known then she had the CMT (the genttic muscular disease she has) I would not have worried so much about it. But as far as mental regression she didn't- at least not due to being around other more severe SN kids.
Her regression came about when her seizures went bezerk.
Now she is one of the lower functioning kids in the class.
- something else you may want to consider-
When we did pull Riley out of the SN pre-k we looked into the most appropriate typical classroom after she stayed home for about a year, she was a young 4 when we looked back into placement (I think, 4) we had her placed into a older 2's (almost or just turning 3) class the kids were right at her level then, physically and developmentally. I had never been really impressed with the school therapy so that was no big loss to her. She had always been in private therapy even when Early Intervention started coming out. Even now in elementary school the school therapy isn't worth what they bill medicaid for.
((hugs))
This is a huge transition for miss Zoe that you have coming up...