Your mom needs to keep her mouth from drying out - try having her gargle the following several times a day - 1 cup warm water mixed with 1 tsp baking powder and 1 tsp salt, I use kosher. Also speak to her oncologist about Nystain oral suspension - When I had thrush, that's what mine prescribed - it really helps get rid of it, and I think you can use it as a precaution as well.
Try having her use biotine products - they have a whole line for dry mouth - I use their tooth paste and mouth wash twice a day, the also have gum and spray you can use through out the day.
Have you tried ginger tea and/or candy for the nauseousness. I find they work really well. If not there are several meds - Compozine and Emend were what my team prescribed to help with the issue. I was lucky I didn't really need them the ginger worked, but others swear by these meds.