Selectively affectionate 7 year old

[ThatHeartyLimeBear]

Advice please - my 7 year old daughter has been cared for by my mum and mum in law whilst I have been at work (either end of the day) since she was 9mth old. Shes now 7. She sees my mum in law once a week routinely on a Thursday after school. She sees my mum on a Wednesday and Friday after school as well as a Tuesday and most Saturday afternoons.
I live across the road from my mum in law but my mum lives 10miles away, therefore she can occasionally see my mum in law across the street if she’s cutting the lawn for example. My daughter is affectionate with everyone; me, her dad, his mum, her uncle and his new wife who my daughter has only known 2years. She’ll openly hug them, ask for a hug from them. She wil hug friends at school and even demand a hug from the headteacher! By my mum (grandma) she point blank refuses to hug, going as far as to say when questioned that she “doesn’t know if she loves her”. She’s the same with grandad (my father in law) who teased her and tickles her like grandads do sometimes.
we’ve put this reaction with grandma down to her not really understanding how it makes grandma feel, but the other day she hugged auntie in front of grandma and then said to her “I knew you wouldn’t like that and it’s upset you”.
therefore there IS intention behind what she’s doing. We don’t know why or what’s set this off.
when she was around 3years old she went through a stage of grabbing me when I would leave her with my mum to go to work and crying not wanting to be left.
this is the only thing we can put this down to at all.
when I’ve carefully questioned my daughter after this comment she made to my mum, her answer was “she started not cuddling her and now doesn’t know how to stop not cuddling her”.
I 100% trust my mum and know for a fact she hasn’t done anything to hurt or upset her. Does anyone have any advice as to how to reverse this.

Also I fully get the bodily autonomy etc of my daughter, but any suggestions are welcome. I had considered a ‘secret handshake’ only for grandma, and wondered if this would help.
she clearly hasn’t got any overly huggy attitude as she’ll gladly hug everyone else.
she says she wants to hug her but doesn’t know how to start anymore.

Can you try and explain it’s hurting grandma’s feelings and while she doesn’t have to hug her, it’s not fair to hug other people in front of her. It’s teaching her to consider others’ feelings. Give an example of something she enjoys and say that everyone in the room would be allowed it but not DD, how would she feel? And say if she wants to start hugging her, maybe your mum can come round just the 3 of you and you all have a chat about it.

I feel like my 7 yo would understand. But maybe have a frank chat with your mum too, she shouldn’t be offended at a 7 yo actions, as she will likely grow out of it.