It does sound like she is having anxiety. Take her to a child behavorial specialist for evaluation as to what, if anything is going on. If she is anxious the sooner this gets addressed the better, as it will only worsen with age. I wouldn't try and guess on this, she is staying upset by worrying about doing and saying everything perfectly which we know is impossible. But in her mind it's very important and you need to find out why. The specialist can best advise you as to what you can do to help her.
This will sound strange, but are you sure that her belly is full enough? I know my child acts strangely when she is hungry. For some reason, children this age will not tell the parent that they are hungry or maybe they do not even recognize the hunger being that their mind is so active. I would first make sure that her belly is full and make sure she is getting lots of sleep at night. If her belly is definitely full and she is getting say about at least 10 hours of sleep and the behavior continues, you may want to take her to a medical doctor because there are some medical problems that can cause excessive crying (not to alarm you). Make sure she her diet is not lacking the vitamin B's (so many of us do not get enough of the B's).