War of the Five Kings
After her father declared himself the true King of the Seven Kingdoms, Shireen became a Princess. She remained on Dragonstone while her father sailed to Storm's End to treat with Renly Baratheon, his younger brother. After her father's defeat and subsequent exile to the Wall, Shireen becomes the head of House Baratheon of Dragonstone.
Surrender of Dragonstone and Later Life
With Stannis gone and his men exiled, dead, or turncoat, Dragonstone lacked the strength to press Shireen's claim. The Castellen, Ser Axell Florent, threatened to resume the war but was overthrown by the majority of the garrison. And so it remained neutral throughout the war, officially surrendering to Renly after the Siege of King's Landing. Shortly after, Renly stripped his niece of her title, fostering her in his court till she comes of age. From there she returned to her mothers home of Brightwater Keep, where she spent most of her days, marrying and birthing children by a scion of the house.