Juicy rrat, is there anything to back that up or is it just a woman moment, and/or /vt/'s social autism taking everything out of context
The main NijiEN general thread has been full of a ton of autism basically since the beginning. The clique accusations at least to begin with generally involved the idea that Elira and her friend group (Elira, Pomu, Millie, Enna, Shu, and Uki all knew each other before Niji) were a clique within the branch. Selen being isolated from them was seen as a thing because in spite of being vtuber "sisters" (both in-lore and by sharing the same character designer) they've only ever had a single one-on-one collab stream (or 1.5 if you count an impromptu collab).
Nina being a bit distant from her genmates early on is something she's admitted to. Millie and Enna were already best friends and Reimu clicked with them pretty quickly. Nina as a bit of a tryhard boomer (by vtuber standards) didn't really have that instant of a connection. However they've been pretty open about this and have said that they did start becoming more friendly gradually.
That being said I find this idea that Nina, Pomu, and Selen will leave because "cliques" to be pretty much just social autism. Nina maybe isn't super close to her genmates, but she seems pretty close to a lot of other members of the branch and company as a whole. Pomu is close friends with Elira, Shu, and Uki from before Niji and seems to have hit it off with Selen.
If Pomu and Selen leave Niji I think it'd be much more likely due to disagreements with management, not internal cliques. Though I will admit that I personally find the idea that Elira and Selen have some beef with each other to be pretty funny.