mother figure 
noun
An older woman who is regarded as a source of nurture and support: a housekeeper named Evelyn became a mother figure to him...
- I figured that it would be easier to find a father figure than a mother figure in this huge city.
- It is particularly important that children have both a mother figure and a father figure.
- When my mother died I was left to be the designated mother figure, looking after my younger siblings, but I really didn't want to be in charge of anyone, not even of myself.