They make fiorocet with and without codeine. Without codeine, it is not a narcotic so is less
addictive. My sister also takes fiorocet with codeine and was addicted as your mom is, she would take them heavily right after her refill, then suffer the rest of the month. I think some people have an "addictive personality" and some don't. The medicine is not bad per se, it just has to be taken
according to dr's instructions. Perhaps she can take the kind without codeine after she gets
over the addiction, or your dad can dole it out, which I do now for my sister and she is compliant.
Triptans of course are an alternative, but not all people can take them. She needs a neurologist.
I take the fiorocet without codeine, have taken it for many years and don't take more than 60 per month, and never run out early. It is a godsend to me, allows me to work, etc. I take triptans, 6-9 per month for the more intense, unmanageable migraines.
Good luck to all of you.