Blue bottle sting help?

this girl got stung by a blue bottle, she was screaming in the water and her friend had to help her out, when she got out she was still in a lot of pain, she started crying and hyperventilating they rubbed some vinegar on it and they took her back to the boat. About 20 minutes after being stung she began to feel really really sick and started vomiting. She had a massive headache and started shaking, why did this happen?!? medical assignment for year 8. thanks:)