User blog comment:B214/Question and Answers 2/@comment-24098614-20140321234015/@comment-9339850-20140321235424

Hasn't happened yet in DxD so hard to say; As it stands in the series, if she was half Angel and Devil, then the demonic energy would corrupt the holy energy causing the person to become a Fallen Angel. What they are trying to do is to somehow keep the pure holy energy from being corrupted.