It's old enough news now that I don't really care about sharing, and third party anyway, but at the time when everything was going down I made a few contacts with people who were in positions to have some level of insider knowledge of how Nijisanji worked (or didn't work) at the time, and it interested me that their attitude was 'fuck everyone involved' rather than 'omg pure perfect Selen was destroyed by evil Nijisanji'. I do not have hard evidence for any of this, but the impression I strongly received was that Selen had spent the last year or so in a severely negative mental state. The people I was talking to had all only worked for Nijisanji within the last year, and all of them corroborated this perception that they had never seen a 'good' interaction between her and anyone else in the company.
Putting the whole timeline together, I would hazard a guess that 2021-2022 were good years for Selen, and afterwards in 2023, she started hitting severe management roadblocks and realized she was in a dreadful situation, and had no idea how to get out of it. As a result, her relations with her co-workers totally collapsed and she severely self-isolated, becoming distant and hostile to other people. We can see strong hints of her mental state in hindsight by looking at how unstable she was when her skills were being criticised in Apex Legends and so on.
I put more and more stock into this concept the more I see the vHoeShow retirees and Mint ignore her on every level possible (aside from Mika, who was a different branch and just has a very forgiving personality to begin with). I think there is severe bad blood there that nobody has talked about or is in a fit state to cope with, given the stuff they've got going in their own arenas. I do not think there are any hideous secrets, massive revelations or dark truths waiting to be uncovered. I just think these women were in a very high-stress, competitive environment and were petty, snippy and catty at each other a whole bunch instead of pulling together in unity, and as a result they just want to stay in their own corners and do their best to forget about each other.