I'm a pro-photographer. These are the questions I'd ask your friend.
a) How big is each print?
b) How are the prints being framed? i.e. matted, framed and under glass (traditional framing) or mounted onto a board with no glass?
c) Who is paying for the framing? You or your friend? If you are framing the photos, and she wants biggish prints matted and under glass, the framing costs could be more than $500. i.e. You lose money selling her your photos.
d) How "messy" is the restaurant? i.e. Is it a fancy place, so the photos will be in same shape in a year, or a sports bar where the photos need to be protected from ketchup/catsup, beer, and other flinging food.
e) Do you need to go out and shoot each photo still, or are you using images that you already have on file?
f) Is she buying the rights to the images? That is... will she be able to use the images on her menus, business cards, website, etc, Or... just have them on display on the walls?
g) Will you get any credit on the images, or are they hung anonymously?
h) Will you have a chance to sell the images on the wall (i.e. have a card with your name and price next to the images or at a desk?) or ... are these images just background filler? So.. are these being hung as art, or as wall-paper?
Regardless, the minimum - if they were a good friend - I would accept is $50 each after all other expenses have been paid (including the printing costs) for each print. With no rights of reproduction included.
You should have a contract with her. Doesn't have to be fancy, just a list of what is understood. Friendships can fall apart on things like this. It's not that one of you is out to "get" the other... you just have bad memories. Write down what you two agree to.
Good Luck.
