catmummy! I was passing gallstones after Ethan was born -- SO painful, seriously I'd rather give birth than go through that again! (Lucky me, I no longer have a gallbladder, so...)
I was kept in the hospital after I landed in the ER for the gallstones, stayed a couple days and then had it removed and then went home. This was like 6 years ago, so I can't remember much about what they fed me - seems I was on a liquid diet for those couple of days?
My husband had gallstones a couple years ago though, and he had to wait a couple weeks for his surgery. He was told to avoid caffeine, coffee, spicy foods, fast food, and all greasy foods.
Hang on... here's a webpage that is more thorough:
https://patient.info/health/gallstones-diet-sheet
Basically, limit fats and sugars - eat lots of vegetables and whole grains, eat smaller meals, and drink lots of water.
How long past delivery will they take it out?