Cum-ala gave lots of nonverbal tells that highlight her level of discomfort. Aside from the inappropriate cackling and smirks: 1) the rapid eyeblink when Pence was calling her (or Biden) out. 2) Gulping - demonstrating she had dry mouth, which is a symptom of nervousness. 3) Pointing her nose in the air - very haughty defense mechanism to cover for a glaring inferiority complex.

In short, the woman lacks confidence and compensates with snark. That repels people.