It is hard to say for sure how to help her, but if her problem is anxiety she might benefit from learning some relaxation techniques. It is good to take several deep, slow breaths while trying to think about calming down. She might benefit from taking pretend "tests" with you at home. See if she does better if she covers up everything except for the problem she is working on right now. Some children get overwhelmed thinking they might not be able to get everything done on time. Ask her what happens during the test. She might be able to describe to you what happens and then you will have something to work with. I hope you figure this out. She needs to experience success so she can gain some confidence in herself.