I’m not an expert on this stuff, but I doubt enzymes would substitute for bile, which is what you’re lacking if your gallbladder is weak, although perhaps your pancreas would produce less lipase after so long on a low-fat diet too. If you’ve never attempted to build up your fat intake, then it seems like a good idea to try. I think it takes around 4g to stimulate bile production, so you could start with a very small amount and increase in 1-2g increments over time.
If ox bile acts as a substitute then I guess that would be useful, but if it doesn’t encourage your gallbladder to function, it’s not going to be a long-term solution. Maybe you can find more info on Google about boosting your bile production. I think your body will respond given the chance, but there could be other factors involved.