The only wee problem I see with Caroline as a name is that there is already a well-publicized Princess Caroline of Monaco. But that would be a problem mainly for the press, having to further identify which Caroline they were reporting on. Otherwise, no problem. Cecelia Caroline would be nice. She might be referred to as CeCe, but that's kind of cute for a little gal or teen, and of course she would have the whole name in use, not a nick-name, when she became queen.
Cecelia Caroline Charlotte Rose (the Rose being for princess Diana). That's a very fancy name which would look good inside flourishes on invitations, with roses and nosegays all over. Very "period". Why not?
It doesn't bother me, if the name is already used by another royal house. Especially if different generations. It would seem odder if they were the same generation, and both would be queen.
Ingrid, Catharina, Leonor (Eleanor), Elisabeth, Estelle, would be avoided IMO, though Ingrid and Estelle wouldn't be on the list IMO anyways.
But if we are going to avoide names already used in royal circles, like Caroline, we will have to take a number of top contenders off:
Charlotte: Caroline's daughter
Elizabeth: Elisabeth is a form, future queen of Belgium
Alexandra: ued in a few place including Ingrid Alexandra, and Caroline's daughter
Sophie/a: Sofia, a form, name of queen of spain and one of her granddaughters
Leonor/Eleanor: used in both Belgium and Spain
William: Guiilliame is a form, hereditary grand duke of Luxembourg, and soon t be king of Netherlands Wilhelm
Philip: two crown princes have a form of it (spain and Belgium)
Alexander: second name of soon to be king of the Netherlands