I think you might be jumping to conclusions, just a tad. The reason she wasn't in the episode could be simply because the director wanted to focus on Usagi, Rei and Minkao the most. I think its silly to think she's too old for the role. I mean, hold old is she, sixteen? fifteen? she's perfect for the role. There'll probably be a mako-chan episode in the next 2 episodes. I hope we get to see her use her lightning rod, or sparkling wide pressure. I never got the name to that attack, what does it mean? I always perferred Jupiter thunder clap zap better, myself.
As for Mamoru remembering Zoisite's name, maybe because Zoisite casted some sort of remembering spell when the scene was shifting from ZOisite's eyes to Mamoru's eyes and then the piano and repeat.