I have a couple of recommendations.
1 - Chemo depletes the body of zinc, you may want to have her take a supplement (from veggies) because without it, everything tastes bland.
2 - Miso soup - is really good to drink as it will alkalinize her blood, replenish the digestive enzymes in her body that are being killed off, and is yummy. I'd recommend a barley miso that is at least 2 years old. When my aunt went through chemo she drank this and really wanted it.
3 - Give her what she wants, but perhaps avoid sugar since it decreases the immune system.
4 - Consider a macrobiotic lifestyle. Elaine Nussbaum's book, Recover from Cancer, details her story on how she beat cancer with a macrobiotic lifestyle, including a diet of whole grains, veggies, beans and sea vegetables. If you decide to follow this path, there are wonderful macrobiotic counselors out there who can help you out.
Good luck and I wish your mom the very best!