Accepted you as the Listener and used your ability to hear contracts to make the Brotherhood stronger. She doesn’t even need to like the Night Mother being there, but obviously it WORKS because you heard about Motierre’s contract, so what’s the harm? Without a Listener that contract never would’ve been heard.

Assuming she sought out Maro, as Maro says: Doubled back on her deal with him by telling you that he knows who you are and that your job was now to kill HIM because he knows the password to the sanctuary and that’s obviously a very bad thing.

Assuming Maro sought her out, like she says: Say no and kill him? Straightforward.

Or; agree but tell you about it and then plan an ambush since he’s very obviously not going to keep his word because he hates the Brotherhood and why would he ever allow them to keep operating if he can just kill you all instead.

To imply Astrid had no choices in the matter is a discredit to her character and supposed position as a clever, savvy Matron. She had plenty of other options, it was just easier to sell you out and hope for the best - two birds, one stone.