I had a bit of a realization regarding the actual size of the bullet that Lilly dodged by managing to not get caught getting two Milestone expansions in succession back at the house. Before, I had somehow thought that the response would be "academic confusion", but now I realize that it would be closer to "instinctive dread".
To Lilly (and possibly the readers), gaining these Milestones is an irregular, but manageable part of her life now. Sure, getting a new Ethos requires a bit of a lie-down just to be safe, but the Milestones are more like getting a crick out of her back: it sounds worse than it actually is, and she feels a lot better once it's done.
To Marius, sensing two Milestones in close succession would probably be akin to the scene in Worm where Noelle experiences multiple Triggers after consuming half of a Cauldron vial. If you have any knowledge of how these things are supposed to work, you can tell that something has gone horribly wrong. This isn't even a "we can discuss this later" concern, this is an immediate "Someone call a doctor, what kind of mutant are you?" situation.
I bring this up because Lilly's just gone unconscious on the verge of gaining a "regular" Milestone expansion, an "super" Milestone expansion, a regular Ethos gain, a Foundational Ethos gain, and some transhumanism thrown in just for fun. Not to mention that Evie's holding back enough XP for both her and [Brave Blood] to level up when she has a spare moment. Hopefully, everyone has decided to "give her space" when she wakes up, otherwise someone's bound to notice the metaphysical explosion that's about to go off.