Hello, My 85 Year Old Mother Fell And Broke 2

Hello, My 85 year old mother fell and broke 2 toes and tore her ligaments in her ankle 6 months ago. She fell because she has had 2 knee replacements and they just gave out. She has had to use a walker ever since and has been in so much pain. It changed her life, perhaps forever. She was prescribed hydrocodone twice a day but her doctor just cut her off, prescribing something else that makes her feel awful. I think she is having withdrawals from her previous medication but the doctor is resistant to returning her to what was helping her to still be mobile. I don't understand why he would do that to her and so suddenly. She is well cared for and trying her best. I don't think she should have to suffer unecessarily, especially at her age. Any suggestions? I just want to help my mom. Thank you.