I know you aren't always into asks, but I would love to hear your thoughts on why it was Marrow's defection and Ironwood's immediate attempt to murder him that finally convinced Winter to defect.
@theseerasures has really already put them into words better than I ever could (see this post, written like three days before Marrow defected and Winter saved his life, thereby demonstrating the exact point of the post), but the short version is: Winter in crisis mode (and she is always in crisis mode) reacts to the things directly in front of her without allowing herself to think about greater implications. Winter is motivated primarily by personal connections rather than ideology. Winter spent all of her formative years as the eldest sibling in an abusive household, ready on a hair-trigger to throw herself on a grenade for whichever younger sibling was the target of father's ire—regardless of if she made herself "the bad guy" in that sibling's eyes by doing so.
So as with everything about Winter, it was actually incredibly simple: she recognized a situation in action that she's seen many times over (now with much higher stakes), and she reacted. Things happen, and Winter reacts. She put on a good show for dad, made an excuse to get younger sibling out of the way, and the moment she was alone with Marrow again and could process what she'd already done—that she had, in fact, already committed treason, for the third time since this started, but this time she couldn't excuse just giving you a head start on account of it would quickly become obvious Marrow wasn't in a holding cell and she had no intention of taking him to one just so that he could get shot for insubordination and desertion later, because even though Winter has made a career out of putting bandaids over cracks in a dam even she can recognize that buying him nothing but a few days and the humiliation of a court martial before his execution was no mercy at all, and for the more practical reason that she would be right there next to him in the firing line now—it was just. WELP. FUCK. MARROW WAS RIGHT. HE SAID WHAT WE WERE ALL THINKING—
(And yes, all thinking, even Harriet's "who cares?" was the most hilariously transparent thing she's ever said and half the things she's ever said are blatant lies about how she feels—you care, Hare, you're just desperately trying to pretend you don't because if you do that means your entire life structure and worldview is a lie and you've been trying to outrun that realization since Gravity because that's a more difficult thing to admit than anything in the entire world, as shown by the fact that in the end you can only admit it when your teammates who got there before you pull your finger off the trigger and then Vine dies for it. I digress.)
—WEISS WAS RIGHT. IRONWOOD IS THE THREAT. WE GOTTA STOP HIM TO SAVE ATLAS. I GOTTA CALL WEISS AND TELL HER SHE WAS RIGHT THE WHOLE TIME. FUCK. FUCK. I'M SO MAD ABOUT THIS.
There's no escaping then, between the previous scene and this one, that Ironwood has become just another Jacques. (Almost like they have the same first name in different languages or something.) And she doesn't repeat Marrow's heartbroken I believed in you, but it's true all the same. But it wasn't the ideological project of Atlas she was truly invested in the way Marrow was: it was the man who made her think he was safe.
Either way, when admiration turns to hatred, it turns hard.