how to get along with such a boss?

My boss is not very nice person. For example, last week she has sent me email and ask me to estimate how long it will take me to finish a job. In her email, there is a request from end user which actually just want to someone to run a script for him. So I have sent email to end user to make sure that is what he wants. He responsed and confirmed my question. So I just copy the script from the email and run for him. Then I called him. After I have hung up the phone, my boss asked me why not notify her first before I did it. I told her the whole task only took me a second. She was not happy and complained me not following her protocol. I feel she is like a micromanager. She wants to show her power. If I said to her "boss, that job will take me second to finish, should I do it?", then she will say "Yes, go ahead". Under that condition, I will have no trouble. However, since I did first, then notify her. She was upset. How to handle such a boss? Please help.