I know I will get a load of replies saying "just take her out" but it's a little more nuanced than that (obviously AIBU is famous for its appreciation of nuance...)
When I started in my current manager role I created a WA group for my direct reports. A colleague Sue who worked for the same boss as me (so same level in the managerial structure) was working incredibly closely with me and my team in a related area asked to be added. I did so, slightly reluctantly as I did want a team space for my reports but at the time we were all working on 90% the same stuff so it did make a lot of sense. So WA was me, my line reports, and Sue (8 people). She got on extremely well with my team and all was fine, having her in the WA group was overall beneficial to bringing the team together.
The WA group was and still is mainly used for "social team chat" eg photos of kids/pets/holidays as well as the odd business relevant topic or chat. It's not used directly for work tasks (we aren't allowed in my company).
Sue has now moved departments, this wasn't her choice and she found it very difficult. She no longer has any work involvement with my team, although she is essentially friends with a few of them. I was expecting she would say her goodbyes and remove herself from the WA group but she didn't and even joked in there about wanting to stay. She was a good colleague and I felt bad for her as I know her move was a bit tough. I thought as the group continued with team chat she'd conclude it was time to sign off.
However here we are 2 months later and she's still in there occasionally contributing but also things such as a team member was recently ill and I sent a gift on behalf of the team, she's asking "what's did I miss" etc. It's starting to irritate me that we don't have a team WA space for ourselves.
If I was reading this I'd say - just delete her - but she is still very popular amongst my team (so yes, I don't want to piss them off by upsetting her unnecessarily) and fundamentally I do feel a bit sorry for her with what's happened, she has found it really hard and I do like her, so if I want her out I need to find a way to either get her to see herself that it's time, or nicely ask her to leave (which I think would need to be managed with those of my team who consider her a friend)
Equally I could just suck it up and let her stay, I'm quite prepared to be told I'm unreasonable having a bee in my bonnet here.
AIBU to want her out of the group? If not, any thoughts on how I can achieve this in a diplomatic way??