mood is on (someone)

[suracta]

Hi in his memoirs, R. Mc Almon transcribes a conversation he had with a woman about another woman while the second is dancing. The first woman says : "Why is she dancing ? The mood is not on her. She is unhappy, and jealous"
The expression "on the moon" is obscure for me. Does it mean that she's not in a good mood or that she has nothing in her life to rejoice or to be in a good mood ?"
Thank You

 

[rrose17]

To me it sounds like an invented expression to say she’s not in the right “space” not in the right mood to be dancing.

 

[ain'ttranslationfun?]

Meaning (not a suggested translation): "She doesn't really want to dance." Perhaps "She's not (really) into it."