Opioid addiction after being in remission 5+ years

My mom has survived stage 4 metastatic melanoma. She has been tumor free for 5+ years. Her various doctors have continued to prescribe her opioids and benzodiazepines along with a long list of other medications. The only chemo related side effects she has now is osteoarthriti. Has anyone else had a loved one addicted after being in remission? She cannot function anymore. Always dropping things, falling, slurs words. I believe she is over medicated per her doctors. I'm hoping she will agree to a detox program soon. I just wanna know if this is a common issue?