Insanity isn't it, Miki has been thrown into a situation where she has had to destroy people that she once called friends almost from the beginning. 

She had to use a Bobcat to run down 100s of people she didn't personally know but recognized. She knew that they were no longer the people they once were before they turned. She saw people in desperation sacrifice their best friends for their own safety allowing them to be swarmed by the horrors without even trying to help; even shoving their former friends towards the feasting fiends.

She was raised to eventually run a huge corporation, taught that those who aren't team players are useless. She sees anyone who lends a hand to the group as her friend and ally. Those who are members of her group are in her view point her family and anyone who threatens that family is a criminal.

She sees the present situation as a national disaster and existing in vacuum of law enforcement. Criminals like those that attacked the group are no longer worthy of consideration as humans but rabid animal capable of acts which are worse than the walking horrors because they can think of what they are doing.