And it wouldn't be anywhere near as much of a problem if it were anyone but Moe. Hell, she would give Momo a bigger pass.
I don't know, I think she would have been furious if it had been any other girl, because she used to be jealous of everyone, but Moeko is at least a close friend, and she wasn't angry with her in this chapter.
I think she's just angry at Ichi because he doesn't spend time with her, but he can spend time with others, and this time he didn't even tell her about the situation. Anna has been holding back for a long time, starting from volume 9, and especially strongly from volume 11, and this situation was the last straw. She doesn't like all the restrictions in the relationship that Kyotaro has started to impose.