The chemo does build up, Jenniferskc, so side-effects often get worse. Sometimes, though, it's a roller-coaster, bad one cycle and then not-too-bad for the very next cycle. So you never know. Make sure your mom is staying hydrated to flush the excess chemo from her body. Also, get her a prescription for "magic mouthwash" to help with the mouth sores. It may be called something different, but ask her oncologist for a script for mouthwash with lidocaine.
Things that have helped others with mouth sores:
Hydrogen peroxide. Swish and leave in mouth for 10+ minutes.
Kefir (a probiotic drink similar to a yogurt shake). Hold in mouth for a few minutes before swallowing.
Switching to Biotene toothpaste.
Orajel Mouth Sore Gel: http://www.orajel.com/en/Products/adult-oral-care/Orajel-Mouth-Sore-Gel
Gum Cancer-X Gel: http://www.gumbrand.com/gum-canker-x-gel-1772ra.html
If it gets really bad, reducing the chemo dosage might be a good idea, especially if it allows her to continue treatment when it otherwise would have to stop. I'm happy to hear her tumors are shrinking!
Tell her to stay strong and hopefully she'll be ready for a liver resection soon!