Answer:
The girl may have a social phobia or an anxiety disorder
Explanation:
The girl has panic attacks when she is around too many people.
Why is that my answer?
First, she's shopping at the mall which does have a lot of people.
Second, she is, at an exercising class and there may be a lot of people.
Note: I am NOT a Doctor, nor am I giving a diagnosis. I am simply giving an educated guess, or at least I'm trying too.