My step-dad's Durable and Medical POAs list my mother for both, then followed by my younger step-brother and older step-brother. My having her POA makes me wonder if am my step-dad's POA by default of my mother being determined incopetent by her doctors and I am her POA, but Durable and Medical.
Without seeing the document, I am only going on what you have written, but as such you are not named, therefore you would not assume your mother's position by default.