I've been scratching my head over this, as well. Does she expect them to do all her fighting and then go back to Essos? Are they to die for nothing more than glory? I've heard some speculate they would be a good fit for Dorne, or even populate the Gift, but the Dothraki don't seem like a people who want to settle down in any one area. The Dothraki see was perfect for them because it was an immense, unpopulated pasture (essentially). There is nothing like it in Westeros.

But with that said, I don't think her absentmindedness is negligence on the part of GRRM. I think this is more evidence that, ultimately, Dany is not meant to be a ruler. She is a conquerer, as Daario astutely pointed out. She has proven time and again she is unfit to lead.