Hi, Judysdaughter,
Sorry to hear your mum isn't responding to her implant. I have no experience of them, they are not widely available over here, but believe me, I know the suffering caused by chronic, severe pain of many kinds.
The best thing you can do is just be there for your mum - read the thread 'Lack of Support' in Chronic Pain Forum. That's all most of us need, or want, from our loved ones - understanding.
Most of all look after your own mental health. It will do your mum no good if you get depressed or become overwhelmed. You can always come on here to vent, or express your concerns.
Dave