Man, I hate to say it because she’s sooooo hot, but I think she was infected by Enchantress and then banished outside by one of Doom’s spells.
Unfortunately, there is some proof that she does get infected… she appeared in the Ultimate Fantastic Four Hardcover Volume 3. You can see Dazzler as a Marvel zombie in the crowd scene where Giant Man says he’d like to eat the female survivors Magento had with him. She’s in the lower left hand corner.