The thing is, even if a knight's blooming is shown in advance on NicoNico, it depends on the whim of the FKG developers, so it can be anywhere between tomorrow or the next 6 months or whenever. The only thing players could do really is wait.
Kerria is actually on the 7th official stream like 2 weeks ago, and being popular among the Japanese (think she was top 20 among the 300+ girls on the poll event) might have been a factor for her blooming implementation.
P.S. by the way, i consider it a "leak" because it's from the FKG official livestream with an actual devs/rep from YourGames JP (the company behind Flower Knight Girl and Girl's Symphony) in it... Arai-san, one of the FKG execs, is sometimes present for Q&A like in the 6th stream.