Anything. You could have said anything. Anything is better than walking away, because you learn nothing when you walk away. You gotta just try something and after a while you'll start to get a feel for what works in which situations and what doesn't.
BUT, to give you actual concrete advice:
I didn't hear the tone of voice this girl had when she said that, but it doesn't seem to me like she was giving any kind of test. It seems like she was just simply saying her eyes are drying out, in which case I would have treated it like an innocent topic of conversation and just kept the convo going. I probably would have LIGHTLY teased her "Uh ohh, your eyes are dry. SOMEBODY was smoking weed on the job. I might have to call security on you. You better behave, missy or I might send you to the mall prison
"If she reacted well to this, then I would have started to qualify and see if she'll qualify herself to me.
"You know, you remind me of my friend Kelly. She's really spontaneous and crazy, in a good way. Are you at all like that?"
This is very light qualifier, but its good because it eases into it. Then, if she responds well to that, I just keep it going, keep the conversation going, eventually ask her a LARGE qualifier ("So what makes, Jessica special?") and then gotten her phone number.
Your biggest problem that you did nothing. If you're not sure what to do, just try to move the interaction forward. A really good default way to try to move the interaction forward is to tease and then try to qualify. Teasing right before qualifying is really good, because when you tease her, you get a little bit of attraction by playfully pushing her away, but then you give her a chance to win it back by asking her a qualifying question.