Upon discovering that her daughter -- a budding guitar player -- liked listening to one of the same songs she did, she thought it would be wise to demonstrate that she, the experienced adult, already knew how to play that particular song on the guitar. Next, she offered to teach her daughter how to play it herself, robbing her of any opportunity to a) learn the song on her own, and b) decide for herself that it was a song she wanted to learn in the first place.
I think a lot of parents could do with a bit more empathy for their teenage children. Teenagers are developing newfound desires for autonomy and mastery, but still feel largely trapped by their circumstances. It's no wonder they lock themselves in their rooms -- it's the only environment they have any control over.