This is exactly correct. Well done.
Once again, this is what you need to do. Realize, however, that the squat may not be completely pain free at this point. She had a knee replacement and things may hurt as she works into new ranges. The keys will be how distracting that pain is and whether the pain gets worse. Obviously, neither of us can feel what she is feeling, but that knee may hurt a little for a while.
If only more people understood this, the squatting world would be a better place.