Since the story will probably have Hime find out at some point, and is unlikely to play this Internal Reveal for drama, it's likely that she'll claim that she knew all along, possibly because she'd come to love working at Liebe.
- That ended up partly being true. Mai’s arm did heal up, and she had to give up the ruse when things got desperate. Hime at first decided she was fine continuing working at Liebe, but then changed her mind to quit. It took a little while before Hime decided to renege on her resignation.
Consider that the Yano family had a Big Fancy House and a maid when Mitsuki was in elementary school, but they're living in an apartment by the time Hime visits Mitsuki in Volume 6. It's possible that they had to sell the house and move away for some reason, thus forcing Mitsuki to transfer schools.
This isn't just due to Rule of Drama, but because their relationship has involved growing pains, with each significant evolution involving conflict of some sort. After Hime learns that Mitsuki is her old friend, their relationship gets worse than it had been after Hime joined Liebe, and after they work out their issues, they become friends. After Hime learns that Mitsuki loves her romantically, she contemplates leaving Liebe(which would almost certainly result in her never seeing Mitsuki again), but eventually comes to accept Mitsuki's Unrequited Love for her. There will likely be another conflict before Hime finally returns Mitsuki's feelings.
Haruko just happens to start around the time Goeido returns, which may not be a coincidence. While Goeido claims that she saw her old coworker Sumika in a magazine, it's possible that was a convenient cover story, and that she really learned about it through Haruko, which could explain why Goeido stopped by on Sumika's day off(assuming she lied about coming to apologize to Sumika and only told that lie to manipulate Kanoko). Haruko's ditzy behavior can come off as Obfuscating Stupidity, and her asking Nene about the schwester system might not be due to her being Innocently Insensitive, but due to her trying to torment her at Goeido's request.
Hime is saddened to hear about Mitsuki being jealous of Kanoko, since she wants the two of them to get along. While Mitsuki is somewhat ashamed of feeling jealous of her best friend's other close friend, Kanoko's antipathy toward Mitsuki is much stronger, so Hime's reaction to knowing that Kanoko hates Mitsuki will be that much more severe. Sumika warns Kanoko that Hime may end up hating Kanoko if Kanoko doesn't get over her jealousy of Hime, so that might end up happening. Depending on how things go, it could result in Hime and Kanoko's friendship being permanently severed, or eventually recovering but not being the same as before.
- The crew all arrive after school, and after clean up, it doesn't appear to be all that late.
- The improv storylines would be hard to keep up with people coming in and out - it would be impossible for patrons to actually keep up, and repeating the storylines would ruin the improv.