Why is the shoulder elevated? Perhaps it's a simple response to the elevated 1st rib and/or neck issue (perhaps aorund C4 region). This is not likely to be the primary cause although you will find cervical problem areas in this situation.

Is there something they are doing that could cause this? e.g. they might be a cellist or tennis player.

In my view you also need to look at the thoracolumbar juction to ensure that there is still enough lordosis to maintain the head over the shoulders and not in front of the shoulders. The later would cause increased upper cervical extension and 1st rib issues etc.

This would then lead on to working on the mid thoracic region to facilitate rib cage and spinal mobility and later, hopefully, posture. Remember that an increase in thoracic kyphosis will by nature elevate the scapula and lead to neck and first rib issues.

It does seem you are on the right track, just keep looking futher afield to ensure they are not back for more treatment 3 months down the track Let us know how you get on