How do you start getting prescriptions through mail?

My mother had fibromyalgia and takes pain medications along with a few other things for her heart, depression, etc. Her pain management doctor is a real bitch, and that is why we are not asking her this question first.

My mother is on disability, so her prescriptions are mostly paid for. How would she go about getting her medication sent to her through the mail?

Thanks in advance for the advice.