Is it possible for her to get custody back when, she has paid no child support?

My husband and I have guardianship of our 20 month old grandson. He has lived with us for 12 months. His father (our son) and his mother both signed consent forms to give us guardianship. Our son, is in the service and deployed and can't care for the baby right now is fine with the guardianship. The baby’s mother has been talking about trying to get custody back. She has only seen the baby 7 times in a year, makes no effort to call him/face time him on the phone, didn't acknowledge him for Christmas, no call or gift, is living with a boyfriend who is bipolar and has acknowledged he has tried to commit suicide 3 times in the past 5 years., has had 6 jobs in the last year and can't seem to keep a job down and lastly only sees the baby if we meet her 1/2 way or drive the 7 hours to her house, and pay for her to get into any event we meet at (Zoo, museum, etc.). We live 7 hours from her and it's a burden on the baby to drive down there all the time as it changes his schedule but we have never told her she can't come see him anytime she wants. She just chooses not to.