Sounds like a pretty drastic for a 17 year old. Do they do WASSCE in the Gambia? If so, what year would you want her to start?
SHS is free here now so she would have difficulty getting into a state sponsored school but there are quite a lot of fee paying ones around who would probably take her. You would have to Google fee paying SHS schools in Ghana but they are quite expensive and you would also have the problem of where she would stay in the holidays.