Learning Mothers actual name is how you escape
Obviously Mother is some kind of monster thing that could run on that logic
But more importantly, Mother has a bunch of children, who can only start to reclaim their identity by reclaiming the names. This is basically how very young children actually form their early identity.
Children don't call their mothers by their actual names but by mummy or something similar. When does that start to change? When children are becoming independent and leave their mothers house.
Thematically it makes total sense that learning Mother's real name severely limits her power over you, just as learning your own name is the beginning of having enough personal agency to even try to fight back.