That really does suck for your mum. Crohn’s is a fucking nightmare. I’m sorry.

I have severe IBS and suspected Crohn’s. My body does not like fibre (any kind of fibre). Most vegetables are out. If I even look at a nut my stomach goes into spasms and I spend all day on the shitter. I eat little fruit. My ability to ‘deal’ with certain foods changes sporadically, too. I gained 30lbs in a year of being vegan, I made great progress recovering from an ED and my stomach became better than it had been in 5 years (all without a majority of what your mum can’t eat, either).

You cannot pin your mum’s problems on high-fibre vegetables and, guaranteed, there will have been other factors in her decline. No human ailment requires the consumption of something that your body just isn’t meant to ingest. 

All that said: your mum’s problems are not the problems of non-human animals. I know a lot of people struggle with this, but: your mum would not consume human flesh/products of human slavery if she thought it would help.