Ah, I'm so sorry. I wasn't sure how severe your daughter's autism is, as so many conditions fall on the spectrum. I've worked as a care assistant at a school for children who were severely handicapped in many ways, some of whom were autistic, so I've an idea what you're dealing with now.
I didn't realise that you were in NY though! I'm shocked that they wouldn't scan you sooner-that sounded like the NHS. I had my DD in the USA, in DC, and I seemed to be offered a scan at every turn. I hope that your OB office is at least being understanding towards you.