What do you do when someone cut Q?

Just happen to me a while ago. Was queuing at Watsons & this old lady just went up to the cashier, annoying the long Q. I was next in line, so it 'sort' of became my "task " to tell her off or at least to remind her she needs to queue.The cashier don't care.

So I sort of "signal'' to her she has to go to the back. Guess what's her excuse? She needs to take medicine, so ........ oh boy..... what can I do.... watch helplessly as the cashier process her payment .
Funny thing nobody say a thing !!!
What will you do if you were me?