Is there a way to control the breathing (the amount of moisture that comes out of her mouth).
You can disable breathing entirely if the condensation effect bothers you. You could also tinker with the breath settings, so that the girl would continue to breathe normally but would
never breathe heavily. Both approaches are potentially disruptive, since there are some Dialogue scenarios which require loss-of-breath (or loss-of-consciousness) as a step in plot progression.
I don't know of any user-configurable options which would adjust the visual appearance of the breath while leaving everything else intact. It would be fairly straightforward to write a Loader mod which targets
BreathMist.