Yes, she can leave

A passage on a carriage wherever she wants to go and some coins are easy to spare, an the least of your concerns. Finding a new maid and test her trustworthiness and her skills would be much more costly, especially in time. And of that, you still had very little to spare. You could make sure that there was no scandal, and regularly check on your bastard, send her sums of money...it would not be a problem. But you better than anyone knew how scary your wife really was. And you doubted that she would mind if you send her away. A nurse for your children would be easily found. You don't know what drove you to make the decision, whether it was loyalty or madness or love or anything else in between.

You nod. "I grant you your wish, Sarah"

It would cause little to no political fallout. Maids changed all the time, sometimes because they messed up or were no longer considered trustworthy or because they wished to marry a man and move into a house outside the castle. Perhaps, you think, it was time to change a few rules, too. With Sarah out of the picture, you could hire a new maid. What a pleasurable experience that would be! The mere thought of it causes a stirring in your loins.

She beamed at you, kissed you. "I will leave tonight, then. I wish you all the best, my love."

You sit there in silence for a while, holding each other in the arms, before she got up and fetched the towels. She dried you off gently, then herself. Helped you to get dressed then dressed herself. You felt a pang of pain, a bittersweet goodbye. She curtsied, like she had always done, and vanished, as servants always do. You had lost this one, this special servant and very special chambermaid. Feeling the need to distract yourself, you decide where to go next.