[If she's maybe a little surprised a moment, it soon turns to a soft, understanding smile, just watching him as he speaks. The way she probably seems very comforted by his words is clear.]
I will remember it. You are a true and honorable man, and a Musketeer's promise will always be a comfort to me... [Softer] I cannot imagine there would be anyone better to have seeing to this than yourself, Porthos.
[It doesn't necessarily escape her that of course his priorities here would also very much center on Aramis. It's not a bad thing, even. The reason he cares is one she shares, after all.]