I wanted to iterate that if she's not big, the SCS might try to work itself out. Just keep that in mind. And the SCS NEED NOT BE TEMPORARY. People have had theirs for many many years. The battery just needs replacing every few years. So she needn't worry about having to have it taken out permanently.
As for the fusion --- this will NOT probably relieve her pain! Surgery doesn't relieve pain. Surgery is only for mechanical problems. After surgery, you're always left with pain -- sometimes the same pain as before, and sometimes worse. So don't figure on getting pain relief from the fusion. It's just not gonna happen. She's still going to have pain.
For pain relief, the SCS is the BEST OPTION. She may still need pain medications, but probably not to the degree that she's taking now. I think i'd go with the SCS if i were her. I just hope she's "big" enough.

God bless and PLEASE keep us posted, will you? Please? My prayers are with you both. Hugs, Lee