What has changed in the child's living environment since custody was decided? It's not about the adults and how they have bettered their lives. It's about the living conditions of the child having changed or deteriorated since custody was ordered.
It sounds like the child is in a stable environment with a stay at home mother. It doesn't matter if she lives at home with her parents. There is a roof over the child's head and the child is being adequately cared for.

