YA fantasy book I read in middle school: something to do with dragons in the subway and a violin player?

I got it from my school library in middle school... this would have been the late nineties, 2000 at the absolute latest.

I'm pretty sure it was set in New York City, though I don't specifically remember where it was. It definitely involved the subway tunnels, I believe the dragons (or some equivalent sort of fantasy creature) used them for transportation?

The main character was a teenaged(?) girl, and there was another guy too, he might have been a gypsy or something? The one detail I remember clearly was that he wore a scarf to hide the mark on his neck that he got from playing the violin. He may also have had the ability to transform into the a dragon maybe?

Aside from those details, I don't actually remember the plot at all.

Though I enjoyed it as a kid, it's not like it was amazing literature or anything... it just drives me crazy that I can't remember what it's called. Searching Google for "YA FANTASY WITH DRAGONS" doesn't exactly narrow the field very much.

edit: solved solved solved