Christabel was a friend of Charlotte Yonge's, distantly related to her through Mary Elizabeth Coleridge, who like Christabel had been one of Yonge's informal society, the Goslings.
The passage describes Christabel as being related to Charlotte Yonge through Mary Elizabeth Coleridge, who was also part of Yonge's social circle. This suggests a connection between these individuals through their shared social connections.