I don't have a problem with the FA using air freshener in the lav - in fact, I wish they would do so more often.

It is possible that the FA overdid it, and used much more air freshener than was necessary. The FA probably realized this (too late) and got defensive when questioned.

It is also possible that the FA used the amount that was required to mask an intense odor. I have (rarely) experienced a lav like that when air freshener was not used, and it was a problem for many people, not just a few.

If my wife was having a medical emergency such as the one you describe, my first thought would be to get her to another part of the aircraft until the chemicals diffused more - if necessary, we would offer to swap seats with two people in the back of the plane. We would have done this before demanding an EMT or onboard oxygen. Yes, we were entitled to seats in F, but my wife's health trumps everything else. If this still did not solve the problem, then we would have looked to other solutions.