6 yr old daughter won't stay with dad

[user1466693032]

Please help!!
My 6 year old will only be left with me or Gran. Hysterical if I say I'm going out and dad will look after. No known issue. Her dad and I don't live together but are a couple. He's upset by this and it's putting huge strain on us. I can't even go to shop for 5 minutes. Not only Dad, but her adult sister too. Cannot give me a reason why, and Is getting worse. She's fine with him when I'm there, cuddles etc. Will only stay with Gran or me.

[eyebrowsonfleek]

Is she ok being left at school, parties and friend's houses?

[user1466693032]

She's fine at all of above. Very shy though, and hates any of us (family) watching her interact with others.