Has anyone experienced a lack of suitable severe arthritis pain relief for their loved ones?

Stress to her doctor that your highest priority is your mom's comfort, not her overall, long-term health. Consider having a palliative care physician be 'in charge' of your mom's treatment. Regular doctors often seem to be unable to see the big picture and, regardless of the situation, remain focused on outcome rather than quality of life.

The nursing home is most likely concerned about opiates causing respiratory depression which could lead to pneumonia particularly with a non ambulatory patient.
Viocodan at that low dosage is not exactly heavy duty pain relief. I would contact the MD and make him aware of the fact that she is suffering and you want her pain relieved!! The NH can give her a "blow bottle" to keep her lungs clear and exercised. The NH can only do what your Mom's MD orders

This may sound odd ....but does the nursing home have a TENS UNIT ? TENS Unit simply sends a small electrical impulse that overrides the pain receptor (nerves) to the brain. Since the TENS impulse overrides the pain receptor, the goal is that the brain will not "interpret" the pain or the degree of pain. This is a "drug-free" solution that many people are not aware or even educated about. How nice would it be to use something that truly works to relieve pain without the cost and side effects?
I was going for Physical Therapy and they used one of these on me for a LABRAL tear in my shoulder and I was amazed at the difference in the pain level after use . SO I researched it and bought my own unit for around 30.00 on AMAZON.COM.
Since then I have used it on my 85 yr old Mother who lives with us for her arthritis pain. I also recently used it for knee pain I started getting and is probably arthritis setting in as I am 60 now. ANYHOW...even if the nursing home refuses to try this , instead of popping pills .....you might want to get one and try it on your MOM on a visit .....and also have it for your own use as arthritis pain will get most of us down the road.
One thing I must warn is : My husband has heart disease and a implanted defibrillator and pacemaker...HE CAN NOT USE A TENS UNIT due to the electo impulses. Luckily he doesnt have arthritis pain . GOOD LUCK !