It takes Cosima a little longer to notice than it might, mainly because she's preoccupied with the mission part of the mission. (The "potential for demon attacks" part especially.) When she does, she waits until after dinner one evening and says casually, "Hey - I appreciate the extra work. Thanks. Is there anything I can do to make that less annoying?"

Presumably beside 'start eating meat.' She knows she may have to, eventually - at least fish - but those are maybe you're in Thedas forever thoughts and she tries to avoid them.