'The test that the court applies is - would a reasonable person who faced the same or a similar situation to your own have acted in the same or a similar manner in the same circumstances. You should therefore only use your firearm for self or private defence if you are satisfied that your actions are reasonable.'
https://mobile.twitter.com/MusingOnMovies
Let's put aside the the specifics of the OP case for a second and step into the common sense corner.
Imagine this scenario:
1. I'm working on my computer in the dining room.
2. My husband is upstairs sleeping in bed.
3. I hear the toilet flush upstairs.
4. I remember somebody broke into my car last week.
5. Therefore, I immediately grab my gun. I'm a woman and feel vulnerable.
6. I run upstairs, and shoot 4 times through the bathroom door.
7. Unfortunately it didn't dawn on me that it could have been my husband who got up to pee.
8. Turns out I shot my husband dead before he had a chance to go back to sleep.
Is this how a reasonable person would act?