She probably has little tolerance; maybe some other time.

You consider, just for a moment, letting her investigate the beverage and discover it's properties, both agreeable and disagreeable, but then decide against it, based on the fact that you're pretty sure she has no tolerance, and you have no desire to explain a very drunk Fiona to the local law enforcement, especially not if she made the decision to jump some poor schmuck in the woods. Though, maybe if that poor schmuck was you... still, though you waver for a moment on that thought, you stick with your decision.

"You... probably shouldn't drink that." In a quick hand motion that you're sure would make Master Miyagi proud, you deftly relieve her of the bottle before she has a chance to partake of it's contents.

She looks disappointed, but relents and let's you have it without a fuss, saying "If you say so, Master."

You smile. "Maybe some other time, though." privately, you make a mental note to poke around on the internet for information regarding Fiona plus booze, and leave it at that; after all, you, her, and the sunset have a prior engagement.