G.B.
Go to the local state offices where people file for food stamps and other assistance programs. They will have the paperwork you need to fill out.
I also suggest you call around and find a support group for grandparents raising grandchildren. We go to one and I can honestly say it's the one meeting per month I just will not miss. I learn so much from the other grandparents! Knowing others are going through the same issues and they are finding solutions gives me strength.
I also suggest, if you haven't done so already, that you file for guardianship. This gives you the legal right to make decisions in this child's life. You can't take this child to the doc, the ER, to child care and more without a court order giving you that legal right. Even a letter from mom giving you permission to do this doesn't really give you anything. You could have written that letter so most businesses won't accept it.
ALL guardianship is temporary. The parents still retain their legal status as that child's parent. When the parent is able to stand on their own and provide for that child there is no legal reason to continue the guardianship.
IF the parent is never able to live and make a home for that child then it is unlikely a judge would terminate the guardianship. The parent has to be able to provide a good stable home for them before a judge would terminate the guardianship.
So guardianship not only provides a certain amount of rights to you it also prevents that parent from coming in and grabbing the child to take them to the current flop house they're living in.
They have to petition the court, they have to pay for the court fees and attorney costs, so since they are often lower income after incarceration/drug rehab they have a very limited income and can't afford to go to court. So the guardianship is often until the child turns 18.
Your grandchild is lucky you were able to take her in and keep her out of the system and going up for adoption.
Find the support in your area so you can find out about respite funds, child care assistance, and other programs grand parents qualify for.