Little is known about Gwynesse's childhood, other than the fact that she was born into House Greyjoy and raised on Pyke. Gelmar Goodbrother remembers that she severed her brother Damron's little finger in a finger dance.
Just before the start of the Second Greyjoy Rebellion, Gwynesse encountered the wreck of Tyrius Lannister's ship and resuscitated the drowned lord. She brought him to Pyke and defended the romantic relationship they had begun, but her brother and Lord of the Iron Islands, Damron Greyjoy, believed Tyrius to be a spy and ordered his execution.
Gwynesse convinced her brother's wife Alannys Greyjoy to free Tyrius in secret with the help of a Drowned Priest named Urron, who wed them on the shores of Pyke after abetting the escape. Unbeknownst to all but a few people, she had become pregnant with the Lannister lord's child. Tyrius joined King Orys II Baratheon in putting down Damron's rebellion, and was killed when he returned to Pyke at the Battle for Lordsport.
After the Greyjoy rebellion, Gwynesse married Loren Lannister, Tyrius' younger brother and the new Lord of House Lannister. Many thought that the betrothal was an act of spite against King Harys Baratheon, though Eddrick Lannett believed that Loren had fallen in love with Gwynesse just as Tyrius had. When Gwynesse gave birth to Tyrius' son, Damon Lannister, Loren passed the child off as his own heir. Eddrick notes that Gwynesse did not return Loren's love, telling Damon that she "only had one heart, and that broke on the shores of Pyke alongside your father's failed charge."
"Gwynesse was bold and venturesome. She never feared the strange.” - Alannys Greyjoy
"A woman who fought and fucked who she liked, a woman who could wield an axe better than my father, a woman who ruled the sea and was the mother of kings." - thoughts of Gwin Greyjoy
"She was a wild thing, more beautiful than any ironborn woman had a right to be. She drove Damron mad with her headstrong ways but her brother loved her ferociously." - Blood and Whispers
"[Damon] had learned early on in his life not to mention [Gwynesse] to his father, it was a topic that turned Lord Loren’s mood sour and ended, more likely than not, at the end of a strap." - Blood and Whispers
“When I first laid eyes on her I knew she would be my wife, Baratheon King be damned." - Loren Lannister
“[Damon’s] memories of the Greyjoy woman were soft things... A coo-ed lullaby, a mane of flowing brown hair.” - Blood and Whispers
"When Eddrick Lannett told him stories of his mother and how she had doted on him, how she never let him from her sight, it filled Damon with an overwhelming sense of guilt that he could scarcely remember what she looked like, how her voice sounded." - Blood and Whispers
“No one could dance like Gwyn could dance." - Gelmar Goodbrother, referring to Gwynesse's skill at the finger dance.
“[Tyrius and Gwynesse] swore the vows as all must, beneath the moon, standing in the surf. He promised her that he would return. She wept like a child in his arms while he swore it over and over again. ‘I’ll come back, I’ll come back to you, I promise.’" - Urron
Loren Lannister, husband (deceased)
Damron Greyjoy, brother (deceased)
Damon Lannister, son
Thaddius Lannister, son (deceased)
Ashara Lannister, daughter