My wife has had 2 total hip replacements, so I’ve been down that road a couple of times now. Recently my mom fell and ended up with a partial replacement (they did the ball but not the socket). I had to sit her down and tell her in no uncertain terms that it was way better to take things easier that you felt you needed to rather than have to work your way back after another fall or other setback, so if she had any thought she might need help she should ask. Her recovery has been uneventful so far, and she’s relied on her PT and OT folks to know how to push hard enough to build capability but no so hard as to risk re-injury.
I hope your friend is getting, and can hear and heed similar advice. Sounds as though they’re doing well so far. Best of luck to them, and to you.