No she didn't. She's crowned as Cersie of the House Lannister. She claimed the throne not as Robert's widow, but as the person who fucking killed the last Queen.The only person who has a true rightful claim to the throne right now is Gendry. The Iron Throne is still technically under House Baratheon since Cersei is Robert's widow and she inherited it via the Baratheon line.
So this has potential to be a huge point of conflict when/if the truth is revealed.
"A Targaryen can not be trus...er you're one too! Umm...group huddle guys ASAP!"