I am 23, female, average build and fairly healthy. How soon do you believe I could fly a two and half hour flight after the removal of my gallbladder?

A week. generally speaking after general anesthesia, and laproscopic surgery, and having a permission from your own surgeon, you could safely fly for two and half hours a week after the operation assumimg you do not have to lift any luggage or any personal bag that have more than 10-15 lbs.
Ask your surgeon. I would suggest waiting 3-4 weeks if there are NO post op problems.