Is it permissible for a Sunni girl to pray behind an innovator, and is it permissible for her to marry an innovator?

Prayer behind people of innovation (Ahl al-Bid'ah) and transgressors (fussāq) is valid according to the preponderant opinion. Ibn 'Umar prayed behind Al-Hajjaj, and 'Uthman said, "Prayer is among the best deeds people perform. If people do good, then do good with them. If they do evil, then avoid their evil." Abu Ja'far al-Tahawi held the view that prayer behind every righteous and unrighteous person among the people of the Qiblah is permissible.

While the prayer is valid, the imams dislike praying behind transgressors, and it is better to pray behind an imam from Ahl al-Sunnah. This applies if the innovation is not one that leads to disbelief (mukaffirah). As for an innovation that leads to disbelief, it is not permissible to follow its adherents in prayer.

Regarding the questioner, congregational prayer is not obligatory for her, and her praying alone is better than praying behind an innovator.

Concerning marriage to an innovator, it is not permissible, due to the Prophet's (peace and blessings be upon him) saying: "If someone whose religion and character you approve of proposes to you, then marry him. If you do not do so, there will be tribulation on earth and widespread corruption." An innovator's religion is not one to be approved of.