How do I deal with disrespectful bosses?

I am in a work situation where I share a nightly task with one coworker who is not interested in helping because she doesn't care much about the job. I addressed the situation with my boss and stated someone else needed to help me with the task without pointing my finger at her. It was a very professional email. He ended up writing me back and stating many of us need to get together to learn the task. I didn't go as it was not required scheduling. I have been performing the task and covering her part of it for many weeks. They have evidence of that in records. What is the professional way of disregarding correction if they approach me on an individual basis?