Complex sentence: In April 2011, DeFer joined the cast of "Gossip Girl", posing as Charlotte "Charlie" Rhodes, Carol Rhodes's daughter and Serena and Eric van der Woodsen's cousin.
Split into simpler sentences: In April 2011, DeFer joined the cast of "Gossip Girl". She is the "presumed" to be Charlotte "Charlie" Rhodes, Carol Rhodes's daughter and Serena and Eric van der Woodsen's cousin.