Interactions like this make me understand perfectly why Gertrude wanted Sasha to be her successor.
Sasha not a cruel person. We see that in this interaction when she takes valuable time to specifically ask about Martin and Jon’s safety. However, she is a person who’s willing to make a sacrificial play. Even after she’s told that it’s “almost certain” Martin and Jon will be hurt in her plan, she’s still willing to go through with it to stop the big bad.
And in all fairness to Sasha, this isn’t even close a Michael situation where she’s just leading people through doors. The only other option she had was to wait around for everyone (Including Martin and Jon) to be eaten by worms, which would have been the wrong choice. Yet, it’s worth noting that A: Gertrude likely didn’t become the way she was overnight, and B: Sasha had an immediate follow through in this situation that I don’t think we’d see from many other characters in the series. In that regard, I can see why Gertrude looked at her and saw the potential for her to be a head Archivist who could make tough calls.
I think it’s easy to see why Gertrude saw so much potential in Sasha, and I even wonder if she saw her old self in her, the person she was when she still had a bit of naivety. I think that’s the most interesting interpretation of Gertrude and Sasha’s dynamic personally, because it makes me wonder who Sasha would have become if had a more time.