She's giving up!

My mother-in-law has been going through chemo for 2.5 months now and is ready to give up. I don't know the specifics of her brain cancer but after her first dose of chemo the Dr. said she was doing well and would only have to have 4 instead of 6 treatments. Still, she is suffering from it and cannot handle it mentally. What should I do or say to make her stick it out?! Survivors, tell me what it took for you to keep on going. Caregivers, tell me what you did to keep your loved ones fighting! Thank you.