I'm too anxious and hesitant to accompany my mother to her mri appointment tomorrow
I can see that you are, what about your mother's MRI appointment makes you anxious?
Her rare disease is genetic and inherited from the someone in my family's line
It sounds like you may be scared about your mom's diagnosis, and that's okay, but you should be there for her. Sometimes when we help others, we forget our own fears and you mom needs you right now.
I'm not sure that's a good idea
Yes it is, be there for here, you will regret not being there otherwise.