You handled this very well Maria. She was probably trying to make you feel bad and having a bad day. I once had kind of similar situation, when a customer from behind me started hurrying me up at a check out, even though the check out assistant caused some of the delay and I had a lot of shopping. She got angry, asking me if I wanted her 'help' and when I refused she started lying about something I said to the check out girl, that I hadn't. Then she started taking my photo! I called the store manager, who didn't seem to care, so I just left all my shopping (€100 worth), and left the store. The manager looked irrate, having to put everything back. It was the principle, more than anything.