Can medical POA be on morphine, etc. and make decisions for a principle?

My sister was named as HCPOA of my now deceased brother. Unknown to us, she was and still is using morphine and other opioids for her pain management. We knew that she had her ups and downs, but when my brother was dying, she went off the deep end, verbally, emotionally, and mentally abusing him and trying to isolate him from his POA's. Conspired to remove property from him before and after his death. On and on. The family was split with total anger on either side. She was making some pretty awful assumptions about family members and clearly made those statements to hospital staff, family and friends. The arguments are still going on, and accusations from her are flying off the rails. She is also HCPOA and POA of our aging mother and now starting to do the same things with her as far and emotional, and mental "abuse" and isolation. I'm not only concerned about her past and present behaviors, I'm concerned about her own well being. I'm only guessing, but think I think she has had a long standing addiction to medications as well as some mental disorder.