If she was crying, I just got really upset and instead of validating, I would do ANYTHING to get her to stop just so I could not be upset anymore. It was a really uncaring thing to do.
Whether it's because it upset you or one is thinking it "fixes" things, "please don't cry" and/or "you shouldn't cry because..." invalidates what the person is feeling. Another good book I'd recommend is "I Don't Have To Make Everything Better" by Lundberg & Lundberg.
