Genissa, Genuissa, Gwenissa, Venissa
According to Geoffrey, Genvissa is the daughter of the Roman Emperor Claudius. Claudius supposedly gives Genvissa in marriage to the British king Arviragus. When Arviragus revolted against Claudius, Genvissa arranged peace between them.
Genvissa is not a historical figure. It’s important to understand that Geoffrey’s work is not based on historical facts but rather on literary invention. His narrative includes elements of mythology, folklore, and his own creative imagination.
Source
Historia Regum Britanniae | Geoffrey of Monmouth, c. 1138