I know you're right and that silence was fine - but it's funny how I felt rude because I didn't verbally respond. I will admit she may have gotten a raised eyebrow from me but only because I have a terrible poker face. I guess part of the reason that I love these phrases so much is that it allows an acknowledgement of the person's position while still maintaining a firm and polite stance of your own. If only I could remember them 'in the moment'....
Well, if she had actually asked the question, "May I please go ahead of you because...." then to not say anything in return probably would have been rude. Whether the answer was "yes" or "no", you should have given her one.
However, that's not what she did. She basically just made a random comment out of the blue. IMHO, If you want something, you need to ask for it. Maybe you will get it and maybe you won't, but when people do that PA thing, hinting around, I think that's just annoying and sometimes is even childish.
I think, if anything, I would have said back to her, "Oh, really?" or something noncommittal like that, as if she had said, "I think they've painted the pharmacy walls since I was last here...I thought they were yellow but now they are pink." Or any other random comment.
But most probably, I would have just pretended I didn't hear her.