I really like this style of parenting that I see here in the US where children are not treated "childishly"; are actually listened to and the parents try and build a relationship with their children by engaging in activities that all enjoy.
I never asked to "friend" my son on social media (and told him why) and he invited me to FB, which I believe he curates pretty heavily and doesn't use much -- basically to make a picture for old people.
He hasn't asked me to friend him on instagram or snapchat and that's OK (and various IG pictures leak out anyway via other channels, like other people)
The adults I trusted and the ones I was wary of I could divide roughly along that axis I think: give me room and I'll feel grateful and proud and super grown up and will try to be responsible, or be pushy and patronizing and nothing good will come out of it (certainly when it was just random adults, not my parents or teachers, I could out-stubborn anyone).
It’s good and important for parents and other adults in teenagers’ lives to keep current on pop culture, but even at 30 years remove I remember how cringe worthy and counter productive it was when such an adult thought that they could relate because of a few radio and tv shows that they watched. Following your child’s Instagram feed may well give a way deeper insight, maybe asking to share their playlists too
I think therein lies a big part of the problem. She's feeling rejected that her 15 year old daughter won't listen to her acoustic cover of some band from her generation, but then doesn't express interest in this huge part of her daughter's generation.
I don't have children so this is just armchair/backseat parenting which I understand is much easier from the sidelines. That being said, it seems very evident to me that it would probably help her tremendously if she would update herself with pop culture and technology a little bit to make herself a more accessible and relatable to her daughter, because playing music from yester-generation is only going to make herself seem more foreign and distant (in this particular scenario)