I probably would have reported her to the manager. She would be the LAST one that I would want running a cash register in my store.
I actually seldom use a coupon, but if and when I do, I don't care whether somebody else likes it, and I SURE don't expect a store employee to give me a hard time about it.
I could tell you about a recent experience I had at Wal Mart with my coupons. The woman (supervisor or something) actually accused me of trying to rip off Wal Mart with my B2G1 coupon! It was a legit coupon from the Sunday paper (as opposed to an internet coupon) and she refused to let me use it!