A female prophet is called (η) προφήτισσα. Even in cases where the male and the female forms are the same word, the article doesn't remain the same (eg: οδημοσιογράφος/ ηδημοσιογράφος = thejournalist).
Aha! I now understand the problem I had. I thought that ´her´ referred to ´the prophet´. But I see it can actually refer to some otherwise unidentified female, whose religion includes this male prophet. Thank you!
The prophet (for example Elijah in christianity) is sacred in my girlfriend's religion (who is a christian). So, the prophet is sacred in her religion. That what the sentence is trying to say. Not that the prophet is sacred in the prophet's religion.