@Violet She might have a noble relative. The children of a noble and a commoner were often counted as commoners, even if the two were married. The "left-handed marriage" specifically addressed this; if the noble groom gave his commoner wife his left hand instead of his right during the ceremony, he acknowledged her as his wife and her children as his, but they could inherit nothing after his death.
Since this agreement would be hammered out in advance, with documents, the groom generally couldn't override it if he wanted the marriage approved. Not just by parents/relatives, but by his overlord/king.
There was still advantage to be gained in being related to nobility, though.
(A noble lady marrying a commoner would likely be cut off.)
