According to Ironlung 4 years ago when the very week Vshojo was created "an agency" contacted her and asked her to audition for their company but she won't say which one. It couldn't of been Hololive because not even a month later Myth debut right? It would make more sense for it to be Nijisanji
Most definitely Niji, as you said, Holo had just had their debut and they wouldn't debut council until summer of the next year. It has been a long-running theory of mine that Niji heard that Holo was going western (the call for EN auditions was in like march? of that year) and they did the whole "rebrand india to EN" in june which in my opinion was a desperate attempt to get ahead of Holo's debut in september, the india thing of course fucking failed so I can easily see them trying to buy out the biggest EN vtuber around to compete with Holo after myth was such an insane success.
Could it theorically have been Holo? Maybe... but the last member (that we know of) which Holo scouted was Polka, who was stolen from the burning remains of upd8 earlier in the year. Holo has not taken to asking people to join after that (to my knowledge).
Edit: I just clicked on the video and WTF is that model? Doesn't match with her squeaky voice at all.