Well it seems more like Bern is in denial when she says that May is going through childish phases.
But she's saying that to give May an opportunity to change, I think.
I don't quite think she's into denial; I'd rather think she knows her perfectly, better than us. I think, she is not implying Maytag's nymphomania it's a "childish phase"; just that, the same that people matures and their tastes change, she hopes May will grow and learn to direct her sex and afection drive only at he, instead of at basically anyone. I mean, c'mon, guys! We
do have "outside knowdledge" that this
actually happens to be the case with Maytag, and we also know Lady Bernadette is the
Great Mistress of the art and science of analysing any situation at a single glance, including people's motivations.
I'd say, Akashayi, that our best bet is that Bern simply deducted correctly that at some point Maytag would have the conversation
we know she
had with herself on that bridge, right before she was attacked by Mary.
Even more, the events of Solstice and their conversation about the portrait, plus Bern's presence in Kin's fateful fight,
armed and fully dressed (if she had just taken her swords and run to help when hearing the fight, she would not be wearing her scarf and cloack; for the looks of it, she was taking a stroll, probably looking for May, maybe even returning from the bridge as this couple has a pechant for bridges!), all those things together maybe, (up to here I'm quite sure; here I'm guesing) just maybe mean that Bern guessed Maytag would be about to take that decission "about any time now".