I think both you and
@thebigt are correct in your comments on this (in my opinion).
I was with my grandmother when she was going through the final stages of cancer (and for her, the end of her life).
The Dr had given her (us to give her) Morphine liquid (or it could have been Demerol, or Dilaudid... Sorry I can't remember at the moment). He also prescribed liquid Atavan.
I honestly feel like the (careful) combination of those 2 had the best effects for her.
Just (of course) be very careful. Those pain meds are dangerous on their own, and the Ativan can add a measure of danger as well.
An extended family member suggested (one difficult day) that we give her an extra large dose so that she could get some rest. I pulled her son aside and reminded him that extra large doses of these drugs are sometimes used to end the patients "suffering" (life is more accurate). So be very careful.
I'm praying for you, your Mother, and all of your family.
I lost the love of my life to cancer. It is a terrible disease.