Hey now! Karla hadn't actually expected this outcome. It was very new to her. New and unpleasant.

"Does it come with extra-strength unconsciousness?" she asked, though it came out more like a groan. "If it does, I'll take a gallon, please."

Apparently, her Black Widow system didn't recognize alien drinks. Which meant she was suffering from the full effects. Her metabolism would still burn them off faster than otherwise, but it wouldn't protect her from the effects that lingered until then.