The blush is precious and Oswin believes she is being a very good person for not saying so. At minimum, it's earned her an extra slice of cake. Assuming it's edible.

"Being honest helps. Being open to ask for what you want, and also knowing you're allowed to say no." She replies, "Emotional involvement?"

It saves her from somewhat snarky comments about how boring knowing all variables in a dalliance must be.