[name_f]Isla[/name_f] goes best I think, but [name_f]Isobel[/name_f] would be better.
I really love [name_f]Isla[/name_f] & [name_f]Scarlett[/name_f]! They sound great next to her brothers as well
[name_f]Scarlett[/name_f] seems to be the most unusual of the 3 these days, originally I was going to say [name_f]Isla[/name_f] but I think it is getting overused more frequently lately