In a sense, I don't have a problem with her per se, I have a problem with one thing she did. She isn't stupid. She knows, and has been sounding me out on a professional basis, doubtless to test the water and see what kind of a reception she gets.
I'm paying her the courtesy of assuming that she does have her reasons. We all do. I had to face off horrendous bullying from a line manager who tried to push me into marking, or to declare MAB before a deadline had been missed, so I do appreciate how hard this is (at the same time dealing with serious personal circumstances myself). I find your colleagues' behaviour in turning against you for a political issue childish, but unsurprising in the current climate. The one who blanked you needs to grow up.
I have no intention of blanking this colleague, or mistreating her, but of simply being very careful not to say anything to her in future which might find its way to management ears. This is surely sensible. But aside from anything else she's vulnerable in terms of her mental health, and I will not be party to any form of bullying of her (and would strenuously resist it if other colleagues tried). At the same time, given the above I think discussing it would be a mistake. It's now water under the bridge and I'm applying the principle of least said, soonest mended.
I know union types can be quite strident and have beliefs they hold with conviction. I'm also mindful that I might have my own very difficult decisions to make if/when it comes to future MAB action. We shouldn't judge, and I try not to. Next time it might be me.