This sort of reaction does not require behavior management or discipline. Your daughter is not doing anything wrong. So, in that sense, the central point is not about what you can do. Sometimes as parents we have to recognize and accept our limitations. We can't always get things to turn out the way we want. Your daughter has a developmental lag in her capacity to handle disappointment. She easily becomes overwhelmed and sad, displaying this by crying over things that most children her age would let pass without such a strong reaction. But, over time, she will develop a better capacity to manage life's ups and downs. It's in that sense that you can't directly help her. Development will have to run its course. There are things you can do, and I'm sure you are doing them. While being attentive and supportive when necessary, also frame things in a realistic fashion: 'I know it feels like a big disappointment, but you can handle it. What can you do to make it better?' And, when she's doing fine, chat with her a little (not long explanations) about how she tends to make mountains out of molehills, that sort of thing. You might take a look at Stanley Greenspan's The Challenging Child. You'll see a section on The Highly Sensitive Child, and will probably ring a bell!
Thank you again.
Indiana Mom