It’s all about the HOTU, my friend:

““…mother of dragons…child of three…three heads has the dragon…three heads has the dragon…the ghost chorus yammered inside her skull with never a lip moving, never a breath stirring the still blue air…mother of dragons…child of storm…The whispers became a swirling song…three fires must you light…one for life and one for death and one to love…Her own heart was beating in unison to the one that floated before her, blue and corrupt…three mounts must you ride…one to bed and one to dread and one to love…The voices were growing louder, she realized, and it seemed her heart was slowing, and even her breath…three treasons will you know… once for blood and once for gold and once for love…”

And again:

“Her silver was trotting through the grass, to a darkling stream beneath a sea of stars. A corpse stood at the prow of a ship, eyes bright in his dead face, grey lips smiling sadly. A blue flower grew from a chink in a wall of ice, and filled the air with sweetness…mother of dragons, bride of fire…”

Plus all of the constant R+L=J stuff in HOTU, which suggests that Dany’s destiny is bound up with Rhaegar’s child of prophecy.