Beneden is full boarding, so your girl will have a chance to meet students from all races. I think will have a better social life if studying in full boarding school.
Benenden has very good pastoral care and this will be an important point of consideration esp. if your daughter is young. As you may know, this.is a very sought after school of UK people. However it may not be an ideal place for city girls as it is quite far from the city area