You need to be on the Dawnguard side. And you cannot ask her about a cure until AFTER the main quest is over. If you ask her about a cure during the main quest she will say it is a gift, not a curse, and she will never agree to cure herself. After the MQ, if you never asked her about a cure, then you can now ask and she will disappear for a few days and come back cured.
Thats why it didnt work for me,i thought you guys were joking,I asked her just to see how she react, to cure herself. when i havent completed the main quest of dawnguard. And now she doesnt want to talk about it. But its okay ^^ I dont want to cure her!Still,its cool. But would be weird to have a non-vampire serana.
