I am sorry to hear about your mum's progress. The lungs get blood from the liver, and so it is not uncommon for liver tumors to progress to the lungs. For colon cancer, it is the norm.
Your nutrition protocol is solid. From that side, there is not much more to do. As far as the enzymes, they are important, but I don't know that removing this one item would account for the lung mets.
The one thing that you might consider adding is H2O2 (Hydrogen-Peroxid) enemas. The portal vein connects the colon to the liver, and getting peroxide to the liver might help to . You need to get "food grade" 35% H2O2. It is not expensive. "Flood Your Body With Oxyge" has a chapter on H202 enemas. Be careful, because you must dilute down well below 1%.
Also, if you can find a clinic in the UK that offers, you might consider H2O2 (Hydrogen-Peroxid) IV drip. It can help with the lung situation.