Along with Marei and Kayla, she is one of the three prostitutes in Littlefinger's brothel who are hired by Tyrion Lannister to service Podrick Payne as a reward for saving his life in the Battle of the Blackwater. Genna and her colleagues are apparently so satisfied with Podrick that they decline payment, much to the astonishment of Tyrion, Bronn, Ros, and even Varys.
|Season Three appearances|
|Valar Dohaeris||Dark Wings, Dark Words||Walk of Punishment||And Now His Watch is Ended||Kissed by Fire|
|The Climb||The Bear and the Maiden Fair||Second Sons||The Rains of Castamere||Mhysa|
In the books
In the A Song of Ice and Fire novels, there is no prostitute named Genna. The only character by that name is Tywin Lannister's sister. This would seem to continue the TV producers' general practice that when they invent new characters for the TV series, they still try to use names from the books which are established to exist in Westeros (instead of making up entirely new ones, which might not sound like they fit).
In the TV series, Tyrion pronounced "Genna" with a soft G, as opposed to a hard G.