My mother had a total hip replacement 30 years ago. What are the signs she needs a new one?

Pain. First, if you're mom had a tha 30 years ago, she already has beaten the odds of needing a revision. She should be getting xrays every few years. The main finding of concern would be pain in her groin or her proximal thigh area. She should have a routine f/u to get an xray and an evaluation with her orthopaedic surgeon. Best of luck.