I'm a little confused here.
She didn't make a defence, she simply said she had made a mistake when dealing with a spider. She admitted the impact was her fault and said exactly why.
She also said she "only realised she had hit the cyclist when she looked back at the road" – meaning she hit something, but didn't know what until she saw him. Not that she didn't know she hit anything.
And for admitting she made a mistake (however terrible the consequences) the judge has shown some leniency as it was not done through intent but lack of thought.
So stop the lynch mob and ask questions of the judge as to why the leniency was applied. The woman appears to have told the truth fairly openly and be very upset about the incident. Put yourself in her shoes, you've made a stupid mistake with catastrophic consequences – of course you'd attempt to minimise your jail time possibly by emphasising the effect it had on you for something you already regret doing but can't change. Its an entirely human response. God, you lot are a mess.