Write Away

I'm just trying to give you ideas to get your brain moving. I know how frustrating it can be to have an idea and nothing to do with it! Sorry, I do tend to get carried away. I didn't notice how wall-of-text-y it was until I posted the comment.

Like above, Person, Place, Problem. They all inform each other to an extent, so start with what you have and build on it. You have your person, you have a great idea for a place, now give her a problem to solve. New York's a wonderful setting for problems, since it's so huge and varied.

Maybe she's new in town (or the area) and is trying to make friends while dealing with her mom, deal with a job, whatever. Maybe she's trying to solve an external problem, like activism or the mean, nasty landlord. Maybe Fiona's trying to prove herself in a career, and has to fight against stigma from being a young, autistic girl.

Maybe Fiona is trying to find the father she never knew? You could get a lot of juice out of that. Like, her mother goes to work or whatever, and Fiona just runs away to find him (which could also involve her mom's POV searching for Fiona!). NYC is a great setting for runaways, too.

Maybe you could try a prompt generator to help you fill in the blank spots?