Have you talked over the issues with your granddaughter.
I have (over more years than I care to discuss) taught many 13 year olds and I have found that is a very good idea to get a handle on what they would like before making any decissions that would affect them.
From the tennor of your post it is possible that she has not had an enjoyable experience in her current
social group or her school environment
You may find that she welcomes the chance to interact with positive peers in a home schooling environment
Certainly if she has been involved with "bad elements" in the past this could be managed much better in the cruising community.
If you do have a discussion don't forget the primary management tool of bribery.
You could find that a willing active crew member
makes the difference between being able to cruise
and not going anywhere. Some careful training may be involved.
I have found that the vast majority of 13 yr olds to be a delight to work with.