Lisa C has the right idea.
Your friend's skill is photography. She gets $100 for what she did for you. My skill is smoking meat and bargain hunting and teaching bargain hunting.
What is your skill? Everyone has one, or should have one. I know places charge a lot for smoked meat. If this were me I'd smoke some ribs or brisket or a turkey and give it to her. If we lived close, I'd do an entire dinner of what I do best. Do you babysit? Do you make a real good dessert? Home made ice cream? My wife has a real good ice cream recipe that has been passed down at least 4 generations. I grow my own boysenberries. My homemade boysenberry ice cream would make B. & Jerry jealous.
Just some thoughts for you.
Good luck to you and yours.