Should I have charged a co-pay?

Usually my crazy-dar works incredibly well, but today it failed me

I'm working Circ at Redwell Waters and a ordinary woman in her 40s-50s comes up wearing nurse's scrubs hauling a small pile of books to check out. Thinking nothing of her attire since we have plenty of medical workers pass through on a regular basis, I proceed to ask for her card.

Me: "Checking Out?"

Crazy Nurse: "Yes, I am. (Points to the pile) Ever see anyone check so many books?"

Me: "Well, our limit is 50 and I've seen a few test the time (Shared polite laugh) Your card?"

CN: "Here ya go"

Me: (Looking at the card) "Oops. Ma'am, this is a health insurance card. I'm gonna need your library card"

CN: "No. That's a Library Card."

Me: "It says Blue Cross right here. (Trying to make her feel better) Don't worry about it. People give us all sorts of cards (Small chuckle to make her feel like not so huge of a moron for a small faux pas)"

CN: "That's my library card. You can just put in the numbers instead of the bar code"

Me: (Beginning to suspect craziness) "Yes, but if you want to check out books, I'm going to see the Big City County Library card. Not this card, which is for something else."

CN: (Starting to get paranoid and frightened) "Why can't you just use my library card? It's got the numbers on it? (Pointing to her deductible amount) See?"

Me: (Wanting to be through with her) "Okay, we switched to a new library card so I'm just going to put in a name"

Her account comes up and, surprise, she's at a group home in the area. I check out the books to her and send her on her way while she's all the while giving me the evil eye.