Sounds really bullshit, but the rrat might actually be a very reasonable explanation for Niji's actions.
The most strange part now is why Niji choose to double down after the backlash from the termination notice in Elira's video, meanwhile in contrast Riku's video takes a more neutral tone.
Let's say it's really some higher management who has a real huge ego and feels offended by Selen/Doki. They would probably stop at the termination notice after they see the backlash (most noticeably HYTE's pull back). Since it's already starting to cause non-"negligible" loss for them financially and if they stop there, they could probably still keep most of their current fan base (excluding dragoons). Riku's video is logical under this scenario. But I find it really hard to reason why they release would force Elira to do her video.
But if for real Elira is the EN side de-facto manager and the driving force of removing Selen/Doki. Then her video makes total sense, because she has to double down. No matter how retarded Niji management is, this level of financial loss would certainly trigger an internal investigation. And under this assumption, what Elira has done would definitely get her terminated and Niji management could actually use this to save face. (Niji good, Elira the bully deceive us) But now after releasing her video, it's quite impossible for riku to fire Elira since she now basically ties herself (and Vox/Ike, likely Millie/Enna) closely to Nijisanji. Even if in the close future, Niji is to treat the EN branch like KR/ID, Elira probably can still bail out in JP as she's quite fluent. So under this assumption, her video is actually the most logical thing to do for her.