Claire

Claire is related to Miranda Bailey.

Bailey's Wedding
Claire was among the group of people at Miranda Bailey's house prior to her wedding trying to get Bailey to stay away from the hospital to get ready for her wedding. When Miranda didn't show up for the wedding because she was treating Adele Webber at the hospital, Claire called her, but her phone went to voicemail.

Familial
Claire is related to the Miranda Bailey family, but it is unknown exactly how they are related.