I am 83 years old. 3-1/2 years ago I had a hip replacement, followed by a broken femur 6 weeks later. That left me with my leg about 2 inches shorter than the other leg. I was told about purchasing built up shoes, etc. I wore lifts in my shoes that helped, but did not make-up the length difference. The results left me with back problems and other aches and pains. Last fall I found out that I could have my leg made longer (NO JOKE). Four months ago the surgeon went back into my hip/femur and made my leg longer. It has made a world of difference in my attitude, being able to stand level. My balance is perfect.
I suggest that your sister see an orthopedic doctor and discuss the option of having her leg made longer.