Hi Kent!

Only about 10% of patients have problems with dietary fat following gallbladder removal (and fortunately, I'm not one of them!). I had my gallbladder removed about 9 1/2 years ago and the only advice that my surgeon gave me was that if some particular food bothered me to avoid it (nothing at all about following a low fat diet specifically because my gallbladder had been removed). However...since your relative has been a low fat diet for quite some time, a more gradual approach might work better; gradually decreasing carbs and increasing fat until she finds a level that works for her and she is comfortable with. Perhaps starting at maintainance levels of carb (60 grams of carb per day or so) and working downward from there.
I also know that there are a few people here who have had problems with the fat content of Atkins following gallbladder removal and I believe that at least one of them follows a lowER (not low) fat low carb WOE.
Keeping both the fat and the carbs low presents some problems with getting adequate caloric intake, but it is doable with a bit of tweaking and if eating a lot of protein isn't a problem for you.