@freedom78 : Having one leg longer than the other after hip or knee replacement surgery is not that uncommon. A friend had a quite significant length difference after hip replacement and has to have her shoes customized with a thicker sole on the shorter leg. And I myself had about 1/2” difference after knee replacement, which threw my gait out of whack, and irritated my already existing Sciatica. I am wearing custom orthotic inserts, which have solved the problem. I wanted to point out that many people have different leg lengths even without any surgeries being involved, and don’t even notice. Might possibly have been the case with me. However, it seems that in the aftermath of a major joint surgery this issue becomes really, really, noticeable. Perhaps your MIL should take this up with her PT person also, since they are very much in the know, and my PT guy was the one to get wise to the length issue, after I had the hip pain etc. Good luck…..