Jenny points out that she totally did say it, quite plainly, at breakfast, but Eric comes running up. Serena tells him to chill -- "Jenny and I are just having our first fight," she says, which I think speaks volumes about just how close she feels to Jenny, and how excited she is about their new family, already accepting this sort of thing as a natural consequence of their lives together as easily as she adjusted to Chuck moving in -- but he's not trying to break it up: it's the party crashers boning in her bed that he's concerned with. Serena gives a great OMG before noticing a girl wearing something from Lily's closet, and charges over to grab Dan. Which again, I think speaks to a flexibility in Serena that is to be admired: even if it was a few tries before it took, she turned Dan into her brother between episodes. You could almost say that her mother's constant marriages and mixed fortunes and the generally radicalized concept of "family" in Serena's life has made her and Eric the ideal landing place for the Humphreys and Chuck.
Even Bart was taken aback by how fast they accepted him, but I love that it was never grasping for anything, never "Eric needs a Daddy" stuff: just accepting things the way they are, right this second, and kind of wistfully wondering when it will all be taken away again. It's a funny little key to Serena that she'll only give you any amount of shit at all if she's already accepted you on her team, or else it's just politeness and the occasional icy eyebrow. The only person she will ever fight back with is Blair, of course, but these things -- getting into a family argument with Jenny, screaming at Chuck in the bathroom, snottily telling Bart she wasn't wearing any underwear -- are signs of her affection: it's the politeness that's the killer.
I mean, I don't intend any of this as an apology for Serena, because I think you only need an apology if they've done something wrong, and I don't think this is a situation where anybody did anything horribly wrong: it's just stuff that happened, that makes sense. You don't need a bad guy every time; in fact, I don't think you ever need a bad guy, because morality isn't relative: saying Jenny is being tacky doesn't let Serena off the hook any more than calling Serena out would make Jenny spotless, and calling Poppy a condescending bitch doesn't really explain why Serena keeps crawling up her cooter.
But I do identify with Serena here even more than usual, because I often get accused of the same thing, and it's not out of a desire to be fake or anything. It's just that there are real people, and then there's the world out there, and it's not worth getting upset with or about people that aren't on your team, because they have no impact on your actual life. It is no skin off my ass to be polite with you, no matter how poorly you're behaving, because eventually you'll go away and things will get awesome again. If she just apologized to Jenny and left the room, that would be deadly. Instead she's willing to tussle, let Jenny in behind the mask, counsel Chuck on his momentary sexual dysfunction, slap Dan and laugh at him in the same moment: those are safe places.