Just as Rhaenyra feared, her throne was usurped.
Now everyone had to chose a side, every single House in the Seven Kingdoms. And she had to gain her supporters, so she sent her two oldest sons: Jacaerys to Winterfell and Lucerys to the Storm's End.
But when she received news of Lucerys' death she sent Jacaerys a letter to immediately come back to the Dragonstone. He succeeded and gained Lord Cregan Stark's loyalty, but there was still one House she wanted support from. House Arryn. But since she didn't want to sent any of her children, you proposed to go yourself.
You are Rhaenyra's aunt, the youngest child of late Alyssa and Baelon, sister of Daemon and late King Viserys, Rhaenyra's father.
Perhaps she thought she'll sent you because of the rumors around you and Jeyne. Since neither of you were married, rumors about you liking women were spread. And the same rumors were spread about Jeyne Arryn.
Now you stood in front of the castle, with your dragon behind you, while Lady Arryn came out of the Eyrie.