My brother (33) was diagnosed with AML on Xmas eve. He has finished round 1 of chemo and is now in remission. He wouldn't eat anything other than cold, sweet fruits when he was getting chemo. Everything else tasted disgusting to him.
One helpful thing a friend suggested was to get protein powder packets from GNC or Longs Drugs and mix it with his drink: milk, or coke, or whatever your mother likes to drink.
Power to you, your mother, and everyone who has ever dealt with chemo. It is an absurdly brutal experience.