I looked at this because while my ex loves our son, he drinks a lot and is not fit to bring up a child.
The law basically says if one parent dies and there are two parents on the birth certificate, then the other parent gets custody, unless
-the other parent doesn’t want custody
– safeguarding reasons- dv, drugs convictions, in prison etc
– a 3rd party like a grandma can show that it’s in the best interests of the child to live somewhere else.
So your mum might go to court and say it is better for your child, to stay in the home she knows, stay at the same school etc.
But wouldn’t your daughter want to live with her dad if you weren’t around? Couldn’t your mum and he do 50:50? How much does he see his daughter now?
I’ve put a statement in my will that if my ex is “unable or unwilling to provide a suitable home” for son, then my eldest sister is my chosen carer, and that she’s agreed to that. It’s all I could do while I’m alive.