So you have a 13-year-old daughter who has experienced some difficult changes over the last year and I think there's two things that come to mind for me. The first is she's at a key developmental point in that she's 13 and entering adolescence. This is a time when hormonal surges create a lot of moodiness in children that is really normal and it's difficult for them and for us to know how to weather those ups and downs of adolescence, but the hormonal shifts of puberty are really important to keep in mind.
However, what you're describing is seems to be much more pervasive. So, you are actually describing the symptoms of clinical depression. You're seeing a long-term loss of interest in things that used to be pleasurable to her, isolation and withdrawal from friendships and from family, numbing behavior, like just watching TV and not having motivation. These are all actually symptoms of underlying depression.
So, parent you are doing a beautiful job of holding that awareness and what you want to do, rather than attending to the symptoms, is look at the underlying issue which sounds like it's depression. You want to be curious when you notice this behavior shift if there may have been a catalyzing event maybe a rejection and a relationship, or betrayal and a friendship, any kind of shifts in your family dynamic, or what's happening globally or culturally to be aware of some other factors that could kick this off. But, in general, it sounds like you may want to help her get to professional support for depression management.