Baby shower etiquette with unusual cirstances?

My SIL hosted a baby shower for me this past weekend. I have heard that you are supposed to get the hostess a gift after the shower, as a 'Thanks'. The issue is, she asked me to take care of all the food and drinks (the full cost). She said she would go pick up the stuff, but wanted to know if I could repay her for everything (she asked me 3 days before the shower). She wanted to pick up prepared appetizers, a huge cheese & meat plate, veggie platters, prepared baking..etc. I just couldn't afford it so got fed up and said I would just do it all myself. I ended up buying and prepping all the veggies, baking until 1am the night before the shower, picking up all the juice and pop, and buying other snacky type things (I didn't buy the prepared cheese platter or appetizers she wanted). I feel that I did a lot of the work for my own baby shower and don't feel I should have to buy her a thank you gift, especially having done all this while 35 weeks pregnant. What are your opinions? Am I over-reacting?