Sarena isn't trying to spite Alex, she's trying to distract him so she can take some shots. She's also definitely not interested in keeping him from doing what little damage he's willing to do, so I object to the description in the last GM post.
Aside from that, I have trouble accepting any of what Sarena's done here as canon due to how much we've skipped over, but with Angel Investor it's really reached the breaking point. Not just because the skipped RP, but also because since after all that build-up, I expected this mission to involve more than just Alex getting in a fistfight with some Alex clones while someone else presses an 'I win!' button. It seems that the mecha team didn't need to pull together and accomplish anything, after all, and it just takes the bottom out of all the fun here to discover that we were rushed along so we could perform a role that was ultimately superfluous, and the super-dramatic event we were building up to turned out to be business as usual on our end.
I understand if we can't retcon all of this out for the sake of a more coherent narrative, 'incoherent backstory' seems to be Sarena's SOP by this point. Still, it's such a stretch to imagine that this all happened as described that trying to come up with a perfectly consistent way to remove Sarena from the plot would be disingenuous and counterproductive. Let's just make it another 'missing scene'.