In Clash, the Undying Ones told Daenerys that she must light three fires, " . . . one for life and one for death and one to love."
The first was quite obviously Drogo’s pyre, which gave life to the dragons.
She will light the second fire in Vaes Dothrak, causing the death of the assembled Dothraki khals, and allowing her to assume comand of the assembled Dothraki khalassars.
All the khalasars will return to Vaes Dothrak...
Daenerys IV, Game 36
And they will become "one blood, one khalasar, one herd." (Daenerys IV, Game 36)
And Daenerys’s babe will be the stallion that mounts the world...
Daenerys V, Game 46 (emphasis in the original)
Of course, Rhaego would go on to die in the womb, another wee Targaryen dragonbaby, the child that Daenerys unwittingly sacrificed to Wake the Dragon. But Daenerys is the Mother of Dragons, and she refers to her dragonlets as her children. If Daenerys returns to Vaes Dothrak and unites the Dothraki, it will be with the aid of her child Drogon. And how will Drogon do that? Dragons are fire made flesh, and fire is power.
Daenerys will return to Vaes Dothrak, "beneath the shadow of the Mother of the Mountains"...
Daenerys III, Clash 40 (emphasis added)
Daenerys VI, Game 54 (emphasis added)