Nutritional drink for IBS sufferer with a PEG tube?

Hello!

My elderly Mother has either IBS or lactose intolerance - possibly both. For a while now, due to other illnesses, she has had to have a PEG feeding tube installed due to difficulty swallowing. The locally available nutritional drink used is Nutricia Nutridrink. However, this gives her immense diarrhea. So we need to find something else (preferably available in Europe, where we live).

Does anyone have any experience with something similar, or have any recommendations? I know I could try blitzing something myself, and I will if needed, but ready made solutions are what the doctors prefer.

Thanks in advance!