Hi Leya,
I'm a peds OT in Manhattan, and while I don't know of anything off the top of my head, I will start asking around for you. You may want to start by asking some of the EI agencies in NYC - call this number - 518-473-7016 and ask for Margaret Adabo. I don't know if she is still there, but this is the Early Intervention Program's main number where you can find out names of agencies in the different Boroughs. From there, you might be able to get a list of providers/clinics near your niece.
If I hear of anything, I'll post it. Good luck,
Sandy