Did they not put a label on it, with Zoe's name and address, plus the name of the medication? They should have, and if they didn't, you should also be questioning that.
It is an easy mistake to make, although it should not have happened, I can understand your concerns, as it could have had serious consequences. Wait until you hear what they have to say before you decide whether to cancel her op or not.
Let us know how it goes when you speak to them.