Movie Etiquette

DEAR ABBY: I just got home from the 10:30pm showing of Harry Potter #4. The first 15-20 minutes of the movie were ruined by the ear piercing shrieks of a baby girl in the back row. It wasn't always crying, although the baby did cry sometimes. Sometimes she'd just start burbling at the top of her lungs. I'm sure it would be cute in a different setting. Every outburst was greeted by a chorus of "sshhhh!" from the people around her, but the mother was just telling her baby "hush now" and leaving it at that.

Understand, I don't mind the odd whisper or cell phone or cellophane wrapper. But this baby was drowning out dialogue, and it would not stop.

So I calmly got up from my seat, walked up to the back row, and asked, in a calm tone, "Do you think she's going to be doing that for the rest of the movie?" The mother said "No", and I said "She really is too young to be at a movie. You should take her outside." and returned to my seat.

The mother followed my advice, and the rest of the movie was enjoyable.

After the movie, however, she chased me down and said "I just want you to know that what you did was very rude."

So my question is, was it rude of me to escalate beyond shushing? Or was the rudeness in presuming to tell her what to do? Assuming it was rude at all (was it?), does one rudeness that affects the whole theater indefinitely outweigh a single rudeness that embarrasses one person?

I understand you didn't witness the context, but I assure you my tone was entirely polite, and the dialogue was quoted exactly. Your advice would be greatly appreciated!