I would be careful always with lumping the lot of people together into any group and saying everyone or even "many" and generalize situations where you assume that people are good or bad or handle things one way or another. Handle your experiences as they come to you and adjust for individual situations accordingly. because 10 marys or joes are jerks to you does not mean that the next person is going to do the same. It has no effect, it's just a statistic and assumption is bad in situations when we're talking about dealing with people in a more generalistic way.

What I mean is don't form your opinion about how you should handle situations like you just dealt with based on a few bad players. Do what you think is right and stick with that. what the outcome of your reaction or handling of the situation whether bad or good should not affect whether you continue to do what you think is right.

Assess the situation and person as you come to it. I can only say that the reaction of the person you speak of should only affect how you handle HER in the same type of situation later. She sounds like a spoiled brat in the work place if you ask me but I'm sure you've had others that do not act this way so it would be unfair to avoid confronting people that may handle it better because you've lumped them in with the bad apple.

As for assertiveness - Keep in mind assertiveness isn't confrontational. Assertiveness isn't aggressive. Assertiveness is something that should be something that shows that you are a strong but honest and respectful person. Most people will react to such constructive criticism as such.