Is it bad for employee morale?

My boss gave me a simple job and even though she is overloaded with work she took the job back from me. I hadn't made any mistakes or even bugged her about how to do it. Apparently letting her know what was going on with it was a bad thing. After updating her she got bent out of shape and said, "just give it back I'll do it." I find this to be unprofessional. Why am I here if they can't rely on me to do something so easy? Is this the proper way for a boss to react? Is there no reason for me to be bothered by this?