This may sound simple, but she should get to know the subway system. It only takes a week or two, and it is by far the quickest way to get around the city. Even if you can afford cabs, you’ll get there quicker on the subway. Especially if she’s going from South Harlem to Chelsea (you’ll see what I mean when you get there).
Seek out local places to eat in the neighborhood. They’re often cheaper and there are some wonderful treasures hidden away all over the city.
I would also recommend a trip to the International Photography Center (ICP). They always have amazing exhibits there and the book store is top notch. Have fun!