In the episode: The storm of Drake and Josh, Helen mentions that her niece had her bat mitzvah. According to Jewish religion bat mitzvahs are for girls when they turn thirteen.
Yeah, I have to agree, I don't see any slip-up there, is she not 13 or something? Because using a couple key words ("her" and "niece"), those words usually refer to the female gender, making a Bat Mitzvahs possible
So the only two things I can think of that would make this a slip-up, would either be that she is not Jewish, or that she is not 13, otherwise, not a slip-up