Self-defence - Use of Reasonable force

Discuss the following scenario.

Dr J decides to tell off Katie for missing three consecutive law classes. K is worried because she believes Dr J when he says he will hang to dry any students who miss three law lessons.

She sees Dr J fiddling with his tie and panics, believing he is going to hang her. Consequently, she reaches into her handbag for her 'defensive' handgun and shoots him. Dr J is dead and K claims it was self-defence.

Break into Law firms to prosecute and defend using appropriate case law.