Does your mum not want to eat anything at all, or is she vomitting food back up that she has eaten? If she is vomitting, then there are meds that may be of help to your mum. But if she just does not want to eat at all then there are appetite enhancers that may be of use. And there are things like nutritional drinks and shakes that my also be of use, Ensure/Scandishake etc. Have you spoken with your mums doctors/oncologist about this? I hope that you can find something that will help your mum here.
My best wishes to you both,
Any advice or comments I give are based on personal experiences and knowledge and are my opinions only, they are not to be substituted for professional medical advice. Please seek professional advice from a qualified doctor or medical professional.