Almost 5 year old granddaughter

I’d let it pass if that’s the term she uses at home.

Now she's legally adopted by him, but it's the girlfriend that makes all decisions concerning her. I'm the maternal grandmother. I also bring her to see her mother often when she has her 2 weeks with me and my spouse.

Her mother was is no condition (ex addict) at the time of her birth, so the baby had to be released from hospital to someone responsible for her. Which at the time (Covid) my ex was with her at the hospital. He took charge from there.

She's been legally adopted by her maternal grandfather (my ex) and we share her 2 weeks there & 2 weeks here. The grandfather's girlfriend wants to be called by her first name. But the child keeps telling me, "sometimes when I'm here with you, I miss my mom", which is the girlfriend. I'm not sure how to correct this without being mean. She very much loves her and has been there since birth.

I doubt anyone can advise without understanding why your granddaughter is confused. What is the ‘long story’?

I think you may need to elaborate a little or we won't know what kind of advice to give....