Yes it is kind of but not really simple. She likely has issues and is selfishly only thinking of herself in situations where she shouldn't be. If you are genuinely feeling sad for a legitimate reason and she acts irritated it is not okay. She probably views you as her pillar of strength and when you are not strong she gets irritated because in some childish way she needs you to be strong for her and she does not know how to deal with it herself.
I could be way off though. Let me ask a couple things.
Is she very insecure?
Is she very clingy?
Does she have moments of somewhat crazy behavior? Like saying she wants to break up because of something tiny like you both having a small argument about something irrelevant to your relationship?
*Gets pen and paper.*
You might not want to go into detail. However let me reiteratethe main point. If you have good reason to be sad and she still does not give you some sympathy and just acts irritated then it is wrong. So long as you are not sad for little [censored] reasons...then it may be understandable. Some girls want their guys ti at least act tough. There is no one size fits all type of deal though. Take of this post what you will. Im just flying off on a tangent here. Sine-ing off....
Everything you said in the first paragraph is true. That is really the issue behind it, she doesn't know how to deal with her sadness so she avoids it, really. But thats just sad, you know? I love my girlfriend. She had a bad childhood for sure, and when she throws up this wall when I'm sad I dont think its because shes being selfish, but rather like we both said she just can't handle it.
As for the rest, yes I would rather not go into detail but I will grant you that she is that 'type' of girl, but that doesn't really bother me. She is definitely the 'crazy' type but she is not crazy. Furthermore I understand why she is the way she is, and pretty much all the time we are golden, its just its a real problem for me when she gets all irritable and stuff when I'm sad. When I feel, I really feel, so its important to me that she is there for me when I need her. Lord knows I am for her. I just don't want this to bite me in the ass later down the road.
If you can't be openly sad with her then you're not being open.
We are however open with each other. This the only area that I can't be open with her. Otherwise i would say its actually a really healthy relationship.