At the start of the vision, we don't know the woman Daemon is kissing and caressing is actually Alyssa. She's clearly a Targaryen based on her hair, but otherwise we don't have much to go off of.

R. Martin's Fire & Blood, the A Song of Ice and Fire companion novel on which House of the Dragon is based, we know that Daemon's mom was Alyssa Targaryen, the sister-wife of Baelon Targaryen and ...