Her brother Kynan Dawes wrote on Facebook: "Kiena was in such a bad place in her head. She took the decision to end what was an awful battle in her life."
He said many well-wishers had been asking where to leave flowers and asked them to do so on railings in Carlyle Avenue, Blackpool, opposite the home of Kiena's mother.
A crowdfunder has also been set up to help care for little Marnie.
These are some of the pictures at the scene in Blackpool where well-wishers have been laying floral tributes to Kiena, who attended Lytham St Annes High School.