Okina here doesn't refer to Miko as Shōtoku Taishi (Crown Prince), but Shōtoku Ō – another name she's known as. While regularly the character means king, 王 in the context of the imperial family is one of the titles used for a male family member. So in this case, it's not "Crown Prince Shōtoku", but something more along the line of just "Prince Shōtoku".
