A strange one I think but possibly more common than I think?
So long story short I am in a trio of friends. We meet weekly, talk daily, very very good friends. Me & one other are closer with each other, we are just more sociable and our friends are very close. The one I am closer with let's call her "Sally" acts different whilst on our group chat compared to when it's just me and her talking.
For example me and Sally will have planned to meet for dinner, she'd arranged it and us talking back and fourth about what she's cooking etc all very happy but at the same time on our group chat will say she's "so done with today". She acts mopey on the group, to the point the other friend is concerned she has depression. It's so odd as when she texts me and sees me she's completely normal, happy as larry. I haven't outright asked why she does this but did pull her up about it over a Christmas party as she was making out on the group chat she wasn't feeling well and might not make the party. But her son was back and fourth messaging me saying she's fine, they were visiting a family member and were definitely coming.
It is really odd! Can someone help me make sense of it please?