Islay, she does really need to discuss the options with someone with more medial experience than most of us. Is her GP approachable and is there someone who could translate accurately for her?
I don't know why she was on steroids for so long, but it is her present problem to look at. I can only speak from personal experience. I had back pain as a result of a wearing hip (still have pain, but now from arthritis) and I had many pain-free years as a result of a hip replacement. Years later, same thing, other hip replaced, same result. Back pain now controlled by osteopath and physio - but they could not have stopped the pain before - and it's not good to take painkillers long-term, in ever-increasing doses.
My surgeon operated on a 90yr.old lady the day after he operated on me.
As I say, I'm no medic, it depends on the state of her bones - an 85 yr-old neighbour had a hip replacement at Xmas.