Ever wonder what on earth you did to make her mad? Ever gotten some version of “You should know” when you have no idea why she is upset?
One possibility is she is feeling unloved by you. You did something, or did not do something, or have not done enough recently to express your love, and she feels hurt. Telling you she feels unloved would be a good way to go, but she wants you to show her love because you desire to, not because she asks for it. (It is just like you wanting her to initiate sex, and it doesn’t “count” if you ask her to do it.)
This is not the only reason she may be mad at you when you have no clue why, but it is a solid possibility.