" Were free flow / free play so theres very little structure for her to deal with and lots of opportunity for self selected play"
This is the single, most unhelpful thing in your setting for this child.
A free flow setting is a nightmare for a child with SN. No structure = no clues for behaviour and expectation. If there's no structure, then the one to one amounts to glorified babysitting, punctuated by support at snack.
Imagine being blind and being put in a strange room. You would seek the walls to know you're boundaries. If she can do anything, she hasn't got anything to work with.
My DD went to a free-flow preschool and she would walk in completely dazzled by the stimulation of all the activities available -completely shut down, but appeared hyperactive. She us now doing so will in her (excellent) special school that MS is crossing her teacher's mind (fleetingly, she isn't at all ready, but is ahead of her peers). If she goes to drop odd her sister at her preschool setting, she reverts to that dazed child -completely overwhelmed with the variety and choice all available at the same time.
Do you use 'choosing boards' with her? Start with two items, one being her favourite, the other one something you know she doesn't much like.
Build some structure into the morning. Do you use music at all? DD's school have a good morning song, song at snack time, song for tidying up, song for lunch - it means that even if the detail is different, or the time is different, the song is the consistency the child needs.
"I very much promote the whole 'sometimes inclusion can be so inclusive it becomes exclusive' attitude so if I do one thing for her all the children have the same opportunity"
I admire this stance, but in this situation, I think it is working against you. It almost colludes with the parents notion that it's all just a little tricky, rather than there being a real issue. If all the children get the same treatment, it's very hard to say 'to cope in this setting, child in question needs x,y,z which is different from her peers'.
Also, the PECS - are you PECS trained? Is PECS being used at home?