I'm sorry to hear about your Mom. I'm sure it has been very hard on you and your brother.
It sounds like you have a lot of things going on, so I'll give you my two cents worth
First, new grad nursing salaries in NYC do run the range you have found, probably a few thousand more if you are working nights, and depending on what hospital you work at. The city hospitals have recently increased their salaries, but are still the lowest paying hospitals, which is probably the $62,000 range. The higher paying hospitals seem to be Presbyterian and Sloane-Kettering. I don't know if hospitals pay more for someone with your experience level, so you would need to find out more from the hospitals here in NYC.
You said the last time you lived here was 14 years ago, which is a very long time and especially for things to change in ways you may not like. Is it possible for you to try some travel nursing job in NYC so you can stay here for a period of time, re-acclimate yourself to the city, and maybe investigate some of the hospitals? "Living comfortably" in NYC has different meanings...some people prefer larger spaces, cheaper rents and will live in the boroughs (Brooklyn, Queens, etc.) and even Westchester, NJ, or Long Island. Others prefer Manhattan and are willing to deal with the small spaces for more money. I think you really need to consider and research this, as real estate in NYC is expensive (as I'm sure you are used to in San Fran!).
I too have student loans in the $40,000 range, but no credit card debt. I have 2 roommates right now, so my salary is great, but I plan to get my own 1 BR in May. I know I will be able to live comfortably on my salary and will start saving to buy an apartment, but for me that means not going out every night, eating in a lot, making my lunch, etc. You need to figure out how you want to live. A lot of people complain about living in NYC and the higher rents, prices, etc., but you get so many things in return (culture, art, music, interesting sights, etc.). I think you could live here on an RN's salary, but you will have to be smart about it and do some financial planning if you want to experience the great things this city has to offer.
It also sounds like you aren't quite sure why you want to leave San Fran...you said you were "stuck in a rut..." Before you pick up and leave the good things you have there (job, support from super, peers) maybe you could spend some understanding what your motivations for leaving are and if moving across the country will actually help. I'm sorry if that sounds harsh (I don't mean to be), but I would hate to see you give up something good. The grass always looks greener...just make sure you'll actually want to mow the grass here!!
Take care and hope this helps. Feel free to PM if you want.