Welcome to YT!~ I agree with the post above about getting someone a living creature as a gift. Perhaps you can design/make a pretty voucher for her (kinda like those Valentine's Day coupon books) saying that you'll contirbute up to $900 to the cost of her Yorkie as a gift. That way she'll know your wonderful intentions. And maybe you guys can go puppy searching together. It would be difficult to find a good quality puppy in that price mark. Especially in NYC.(I live in NYC area also) I think it's very thoughtful that you want to help your friend find a puppy as a graduation gift, but like someone said above, it might not be the look, personality she is looking for. It would be better for her to pick it out herself. And if you guys go searching together, perhaps she can find a puppy for $1400 ish, and only have to pay $500 out of pocket for herself towards the puppy.
Good luck on your search.