Board Thread:TV Show Discussion/@comment-36405009-20180731152220/@comment-32860540-20180811020751

Most of Daenerys’s fleet was destroyed, not all. She still had some ships stationed at Dragonstone which should have been enough to ferry the Dothraki and their horses to the mainland.

Also, I doubt all 100,000 Dothraki and their horses were at Dragonstone considering it’s not that big. I think some Dothraki were already on the mainland and Daenerys just led them to attack the Lannister army.