GAD,Bipolar Disability

I'm a teacher. I have General Anxiety Disorder and Bipolar II. I was given
a written warning by my supervisor for missing a half day staff development
eventhough I called it in as a sick day. This incident has aggravated my
medical condition and I was told by my doctor to take time off for therapy.
I do not want to go back to the same campus for fear of retaliation because
I filed a greivance against her. I have requested to be reassigned to
another campus. What recourse do I have?

Fear of retaliation itself may not suffice.
If there is any inappropriate action then you could take steps to have her disciplined or fired or take other actions