My heart goes out to both you and your wife. She's fortunate to have such a supporting husband and it's great of you to be here looking for feedback.

If most of her pain is localized in her legs, heck, go for the SCS trial. It'll certainly give her a good idea if the stimulation will cover the pain. I find the stim to be very soothing on my legs - a far cry from the horrid burnin pain.
If her pain is spread elsewhere, then it might be better to check into the pain pump.
There are quite a few hoops to jump thru (in most cases), but well worth it if it works out. I'm hoping your insurance would be willing to cover this.
I'd certainly say that chronic pain to this degree IS INDEED a medical necessity!!

Caring,
Rae