I know there's been a lot of variations of Clair's name ever since Umineko first introduced her, but the right one is Clair vaux Bernardus, since she's supposed to be based on Bernard of Clairvaux. Her name is written as クレル・ヴォーブ・ベルナルドゥス in Japanese (Kureru Vōbu Berunarudusu).
Updated by jxh2154