Some background: Dd(21) is home from uni for xmas. She's great friends with a our friend's dd (20) who is also home. We've known the family for over 20 years and now socialise about once/month with the parents.
Over the past couple of years, she's been sharing small video clips/pics/stories of her life with our friend's daughter. It's got worse in the last year. We find out from our friends that they know family stuff. It sounds so minor but it has begun to increasingly irritate me. So, any family things we do seem to get passed on to this friend who then tells our friend's daughter who then shares it with her parents who then disclose they've seen us in video clips/pics/what we've been doing.
To give an example .. we were out driving to take a walk the other day, all singing a bit daft-like in the car/bantering/making jokes, etc. our friends popped over the other night and turns out they'd seen a videoclip of us doing that which she'd sent her friend. In itself I guess it wasn't a major thing but it just felt a bit intrusive that they'd had access to it unbeknown to us and her sister. There has been multiple other similar incidents.
I've tried speaking to her and she just gets annoyed but I'm starting to feel what happens in the home isn't private any more if you get what I mean. I feel she's using what we do at times as comic capital - not in a nasty way - but because her boundaries have become so weak.
So, how do I resolve this situation. I've told her already that I don't feel comfortable about it but she is defensive and eye rolls. I've told her in the past that she shouldn't do this but I now don't have any confidence in her ability to maintain that private-public boundary and not overshare. It's akin to young teenage behaviour rather than a 21 year old, I feel.
Just to add, there's nothing romantic going on between her and this friend.