From what you describe, it sounds as though she was criticizing your piece for a very superficial reason. Your response was entirely appropriate.

I likewise condescendingly use the term "I'm sorry you feel that way" when somebody has made a ridiculous or unfounded allegation against me. And, if I was saying it to them in person, my voice would be dripping with sarcasm. That's intentional.

What I object to is when people use it to try to "trick" someone into thinking they're being sincere, but it's quite obvious that they're merely being condescending. That's an insult to our intelligence.