House of the Dragon: Why Did Vhagar Abandon Aemond?

One of the most curious events in this episode is the disappearance of the dragon Vhagar, who apparently abandoned her ailing rider Aemond at Harrenhal to go on a countryside spree while he recovers from his stab wound in the care of the enigmatic Alys Rivers. But as Aemond, as out of it as he is, correctly noted, Vhagar would never just leave him.