@nao48,
She's 15. She might be telling a lot of people that she loves them, when what she really means is that she likes them a lot, or she's grateful to them, etc.
If it bothers you that much, you can always tell her that you're getting mixed signals from her, and that it's confusing to you. But be prepared to be told that she "doesn't mean anything by it".
PS Don't try to break a couple up. Even if he is a louse. She will figure it out, or not, on her own. Unless he is actively abusing her,
stay out of it.