@Cielaevatein I doubt it. Maki made it a point to hide it from her, and she seems to trust her a little too much, not even picking up on her tsundere tendencies in the main series.
I don't understand the last two panels. I wished they translated the flashback dialogue. I didn't understand the context of towards Karen's feeling then.
@Karsh Because they promised each other advice on love? How does this give you yuri vibes? Yes, it is very likely that Erica has a crush on Kaguya, but this chapter is about another.
@VesperPie They make fun of Erica's uselessness in romantic affairs.
Probably the same way that people reached the conclusion to romantically ship characters like Kyouko and Sayaka from 'Madoka' or Gabriel and Vigne from 'Gabriel Dropout'
@Karsh We have apparently different views on what can be called "yuri vibes". I prefer to separate the usual best friend ships and the explicit ship bait / teasing as in the case of Kyoko x Sayaka. Otherwise, we will have to conclude that any friendly interaction between female characters is yuri vibes or subtext.
For some reason I didn't pick this up when it came out even though I read a chapter or two so just read it all recently. I don't know what I was thinking. Really captures the same feeling well.