Hi basildonbond. So sorry to read this. How is your mum doing? I came across this thread because my mum is suffering the same thing. She has a horrible rare cancer of the uterus which has steadily worsened to the stage that she now has cancer throughout her peritoneum and elsewhere.
What has shocked me is how quickly this has deteriorated. She was with us at Christmas, and although she was having real trouble with eating and was in some pain, I didn't think she was as bad as I expected. She is due to start palliative chemo next week and we were assured that the couple of weeks over Christmas and New Year would make little difference.
Well honestly I cannot believe how this has developed over the past week and a bit. Mum has spent the past two days solid vomiting with horrific levels of pain. She can't keep anything down, not even water or tablets. She's now got district nurses coming in three times a day to give anti-emetic injections. I'm terrified for her. My Dad reckons that she can't have a total bowel obstruction, because she managed to "pass" something yesterday, but it must be getting pretty close to this.
A couple of weeks ago she was given 3-4 months if she opted not to have treatment. It seems to me like things have developed substantially since then, and there's now a big question mark over whether she will even be able to start chemo given how much the past few days have weakened her.
I find myself wishing for her sake (and if I'm honest all our sakes) that this will be quick and that she will not linger in this amount of pain for another 2 or 3 months. I wish I knew more about what to expect. It's not helped by not being there. I was planning to go up next weekend after her first chemo treatment, and once every two or three weeks thereafter, but now I'm thinking that I might need to be up there sooner and for longer. No one seems to be able to say at the moment. A bit of an essay, sorry. 
Basildonbond - if you want to talk then do feel free to PM me. xx