I also think that your main flaw was in the nature of the comment you made. If you had rationaly explained, i.e: 'excuse me but you're blocking the aisle, others need to get their groceries through too', there may have been no confrontation, thus improving things all round. You complain of her rudeness, but what you did could be conceived as of being even ruder!

I do think it's good you stood up for yourself though, just try to keep it cool!