I need help getting guardianship of my grandchild whose mother lives on the Flat Head Reservation

My granddaughter is 13 yrs old & is currently living in an intensive treatment cntr. Her mother has given her pot & tried to get her to start smoking. Her mother told her that she hopes she never gets out of the treatment cntr. She allowed her daughter to be molested by a relative that lived with her. He did this to 4 other members of her family. She has allowed her boyfriends to touch her inappropriately & attack her physically. My granddaughter slept in her clothes & shoes, so she could kick out the screen to run and hide. Her mother even told her not to mess up her chance to get married again & just don't make a mess of things. Her mother lives on the Flat Head reservation, she is 1/32 native. I'm 1/2 Native and my tribe has federal recognition. My husband is 1/4 native, as well. Our son agreed to let us have guardianship. We & our son lives in Virginia & she is in Montana. My husband is a disabled veteran, so we are limited on funds. We need immediate help. PLEASE!