D.K.
I've had a niece and nephew BOTH with not being able to handle things. Both are now grown and the "problem" was something that they eventually outgrew. Josh threw up EVERY time he got himself worked up or feared something....anything......even things like being at swimming lessons. HONESTLY, I"d rather have one passing out than throwing up constantly! LOTS less messy!!
There ARE people who faint easily. She may be one of them. Give it some time. Talk about how she feels, why she feels that way, what things she might do to overcome those feelings, etc. Remind her how powerful the mind is, ESPECIALLY when it comes to overcoming and dealing things.
There are great children's books out there that deal with just about EVERY life situation, including overcoming fears, etc. I used to work at a children's bookstore so I KNOW they are out there. As a librarian to help you find something for her age level.
My niece, stuttered. Kids have their way of dealing/not dealing with things that make them feel uncomfortable or out of control. This was frustrating for EVERYONE, including my niece. The doctor said her cognitive level was far ahead of her emotional and physical level and this is what caused her to stutter. She DID outgrow it, so did my nephew. He's now a sophomore in college and doing GREAT!