We've noticed, thanks to a re-listen of The Hedge Knight, that Egg points out his mother, Dyanna Dayne, is dead.
There is no mention of Maekar I ever remarrying, nor is one listed in the Targaryen family tree in The World of Ice & Fire. So... Westeros seems to have been Queenless for the entirety of Maekar's 12 year reign.
12 years without a Queen, that's interesting. It raises the question of the role of queens in general. There are queens of many kinds, some that were awful(Cersei), some who were amazing (Good Queen Alysanne), some who had little direct impact on politics (Queen Naerys), some who wielded power in large amounts openly (Queen Visenya) and others who wielded power in large amounts behind the scenes (Queen Alicent).
Margaery is surely doing exactly what Cersei fears, winning Tommen over. She would be a powerful queen, though will she get the chance?