Hi Earthly One, does your sister eat low carb?
Because my partner and I both used to get major flare ups of our IBS with fatty meals, but surprise, surprise, all symptoms disappeared when we switched to low carb. It seems it was the combination of starches and fat that caused the problem(s!). Our meals now are quite high fat - no problems. My partner eats starches from time to time, and will have IBS symptoms just about every time. (I say it serves him right for being silly! )

And just to go back to the topic, yes, some folk minus their gall bladders do have "issues" with fat. They can still eat low carb but have to be more careful with fat intake.

Rosebud