Rosalie de Hemricourt de Grunne is actually a witch of Belgica, which is the Strike Witches equivalent of Belgium. Although the interesting note is that she is the heiress for two families of earls, one being Gallian and the other one being Belgican. She also apparently has the right for the Britannian crown due to family ties of nobility, although that relation is quite distant it seems.
So Rosalie is a noble witch of Belgica with some major connections.