Im sure there are much more knowledgable people on here than me, but I have heard peppermint tea can reduce chemo related nausea. Also I have heard not to eat when people are going through a nausea phase. Try juicing vegetables raw, and drinking that instead of having solids, this should provide essential nutrients.
Tell your mum to take extra vitamin C (Solgar ascorbic acid crystals) or echinacea to boost her immune system that is obviously suppressed with stress levels.
I understand totally what you are going through as my mum has cancer too, and is on chemo, although her main side effects are tiredness not nausea.