KitePower has nailed it...
Controlled weight or resistance style rehab exercises
MUST always follow this type of trauma to the joint. More specifically as others have expressed there is a time factor (if rehabed) before full rotational use
MAY be regained without discomfort on certain angles..
Essentially the new
1 day old nerve endings that grow & control muscle / joint movement, will not know how to stabilise properly unless trained (This is why a rolled ankle wants to keep rolling for a while)
It is the nature of our sport that we fly in gusty (not constant) winds - getting used to bending the knees to "instinctively" absorb this effect will further reduce the Shoulder strain tendancy.
It is also true that younger people (u18) will normally recover faster,
and also true
after the third Dislocation - the joint will never quite work the same again !!!
So the questions she should consider are:
1. How long since injury - more the better..
2. Physio or rehab training - without the joint will be quite weak
3. Kiteboarding is fun and will always be there for her - if she needs more time.
4. Please take advice from QUALIFIED rehab people - its preventative medicine
It is a nice gesture

to look after your friends, without saying
.............................She'll be right mate............................
Cheersz