That would be a logical failure on your part.

GP said: "Maher? Like Bill Maher, the Jew? So she's a Jew."

It's the most basic logical construction. The connection between Katherine Maher and Bill Maher, as identified above, is the name Maher.

If P then Q.

If last name is "Maher" then person is Jewish.

Maher being an Irish name, that is false. Attempting to claim that Katherine Maher is Jewish, solely based on her sharing an Irish last name with Bill Maher, is a failure of logic. And wrong.