I'm sorry I don't know of any specific grants for helping out your mom. However, if you haven't already done so you should check out theNational Kidney Foundation to see if they can help you, or point you to other useful resources. Learn more at www.akfinc.org or at helpline@kidneyfund.org.
Sometimes people with serious medical bills and a story to tell get help by crowdfunding -- that is, they tell their story on an internet portal for this purpose and other people pitch in to help out. One site that is specific to health and medical issues is gofundme.com. Discover more about this and other crowdfunding sites in Free Money 2015.