Going by the vision she had in the House of the UnDying, the three heads of the dragon are shown.
Rhagar dying on the Trident
Viserys being given his golden crown and
A man with long silver hair, looking back over his shoulder at a burning city ( she does not see the face and assumes its a male). A banner of a Fiery Stallion flys overhead.
I think that is Dany seeing herself at some future battle.
She and Drogon are the Stallion that Mounts the World. That's why the Crone(s) looked afraid, probably had a glimpse of Dany's True Children.
Dany will soon have all the Doths in her Kalazaar so I think she will use a Fiery / Flaming Stallion as her personal banner to fly alongside the Three - Headed Dragon of House Targaryen.
What I'm hoping we won't see is the Fiery Heart of R'holor. Dany's already been burned by magic twice, I don't see it happening again.
Dany learns her lessons the hard way. MMD and the Warlocks/ UnDying will have taught Dany enough about those who practice magic to keep Morq at arm's length. Quaithe on the other hand? Who knows? So far she hasn't asked for anything so she's probably the most dangerous of all.
One thing I can't see is Dany falling under anyone's spell ( besides Darrio
, but I think that's just cause she lonely and he's a slick talking bad boy -( been there, done that).
She wore the floppy ears and tried the meek and mild path in Mereene.
She gave a crown to a Son of the Harpie and took him into her bed to buy peace and they paid her with false coin. That won't be forgotten but it did Wake the Dragon so Dany is now a True Targ, a Dragonlord / rider. So Mereene was worth it after all. Another lesson learned that will serve her well in battles to come and Westeros.
I think the other dragons will be controlled via magic horn and warging. It's possible that someone with Targ blood and courage could become a rider. I've cracked potted all over the place about the idea that Quenten could be alive and trying his hand at that now but it's slim - slim to none truthfully but this is GRRM so as I oft repeat - He could make something like that work.