It's not what you think, how you think. She has not had a perfect life. You've heard of her - heard of her parents, at least, assassinated in the Purges while she watched, screaming and shielding from the Hounds that then turned on her - until he rescued her, brought her home and kept her safe.
And she grew up safe, with a tower full of protective "big brothers" and, eventually, lovers. She explored and sang, and her laugh charmed all who met her...
Don't think she doesn't remember. Don't think that she doesn't wake up some nights with the image of her mother literally torn limb from limb burned into her brain, fist pressed against her mouth to keep from screaming.
But she knows she has two choices - curl up and die or keep walking. Two choices - laugh or cry.
And she laughs, because there is so much joy, because she trusts that things will be all right, because she sees the beauty in the small things, the beauty that always, always surrounds her. Because she loves and is loved. Because this is what life is. Because this is who she is. Because there is too much joy to be contained in such a small person... she dances.