My DD 14 is going through a very similar thing and like yours seems much happier! I also make sure we do something each day together outside.
She's had two really close friends since Y7 but a new 'popular' girl has started to include these girls in her crowd but doesn't get on with Ava. She's actively tried to stop them being friends with DD but they're loyal and still see her on their own. I think they do spend the majority of their time in this crowd now though unfortunately.
I've also been getting her on the cross-trainer daily so she will hopefully have had a 'glow-up' as she calls it, by September!
I also, for a number of reasons, spent most of my 16th and 17th years without seeing friends and, although I wouldn't describe it as the happiest time, I never remember having FOMO strangely. I just knew it was something I had to do.
My parents then sent me nannying in the US for six months and I came back a lot more confident and my social life then took off.
Like others have said, your DD is being sensible and mature about this and, if she seems happy, she's doing the right thing for her.