LogFAQs > #961737715

IDK, I feel like Drummer's decision-making was fairly consistent if not explicitly handed to the viewer.

She was on a personal mission to end him because he killed Ashford and she felt responsible for that and all the death he had caused because she had him dead to rights before and made the decision that he was to live. So she was on her pirate/sabotage mission and when she saw strategic opportunities to screw him over further she took them (allying with the splinter faction, raiding his supply depots) culminating in her taking the supplies to Ceres to massively undercut his support at a key point in his war. This inadvertendly made her a hero among non-Inaros loyalists.

Avasalrala noticed that and saw that if she could get Drummer to publicly ally with her they could divide the Belt and basically create an official non-Inaros Belt faction to treat as the "legitimate" Belt rather than it just being the Free Navy. Drummer told her to fuck off though because she very much did not forget nor forgive the Inners for their past transgressions against the Belt, especially coming from Avasalrala of all people - seeing it for what it was, an obvious play by the Inner Planets to use the Belt against other Belters when it was convenient for them.

So Avasalrala goes to Holden to try and negotiate for her instead and ends up telling him about the railguns in Ring Space and how Inaros is heading there and if he does then he can sit safely entrenched in there for pretty much the rest of his life and he'd have all the colony worlds at his mercy and able to supply him indefinitely so they couldn't even try to just siege him by blockading the Ring. So now Holden knows there's a very immediate time pressure on the situation. Now the following takes place off screen but I think becomes pretty clear at the end of the last episode - Holden (and probably Naomi, mostly Naomi probably) goes to Drummer and tells her that. Now "kill Inaros" still isn't a good enough reason for Drummer but they foresee the obvious Ring negotiation thing happening once he's dealt with because they need to set something up to manage the whole "there are things that will eat people and ships if you mismanage Ring transport" and concoct the plan to form the Transport Union with Holden as its head because the Inner Planets will go for that... only to secure Drummer as VP, etc. in writing with the intent to immediately resign to put the Belt in control of it.

Like Drummer was motivated by revenge and then ultimately only joins the Inner Alliance at the end there because she and Holden (and she only likely listened to Holden because of Naomi) hatched the plan to create and then steal the Transport Union out from under the Inner Planets and end the cycle of Earth and Mars treating the Belt as second-class citizens who can never hold any real power because revenge against Inaros alone wasn't enough for her to overlook all the shit the Belt endured for her back when it was Avasalrala making the pitch.

And even then Drummer had to be broken down by Naomi at the end of Episode 5 because of how much she hated the idea of going along with the Inner Planets even for the sake of stopping Inaros.