I've always said no when she asked, always. She's been a lot more persistent lately and I'm trying to come up with an alternative.
It hardly sounds like that, when you begin this thread questioning if you can let her do it. And then mount a defence for why you’d allow your daughter to call another woman (who funnily enough doesn’t have a strong relationship with her so it’s not actually on the cards!) Mummy.
But I think you're taking the whole birth thing a bit far. The people on this post saying unless you gave birth to them you can't be their mother really obviously haven't experienced blended family dynamics.
Erm. Right. Well you’re wrong about that. And whilst you can help parent her, and be her step-mum, you’re not her mum - not because you didn’t give birth to her but because that role is already taken. She doesn’t need a new mum she needs a good step mum.
My first husband died and my older kids have a loving and devoted second-father. He’s more than their stepfather, as after our marriage he adopted them, but we always dissuaded them from calling him daddy or even dad. There are loads of words that imply a loving parental relationship; he didn’t need one that was already taken, and once that was firmly but kindly explained the children immediately accepted it and came up with a different name.
Their darling daddy gets to remain their daddy, no-one in the family gets confused by who is meant when daddy is referred to, and DH2’s loving relationship with them is acknowledged.
Your step-daughter hasn’t been bereaved, but to she’s had a lot to contend with in her short life, with her parents breaking up, her daddy getting into a new relationship, and him moving her into a blended family. It’s no wonder she’s confused, and you all need to support her with working through the uncomfortable realities of the family situation, not confuse her and cause upset with her mother.
I hope her father would have put his foot down over her calling you Mummy. 