To the jacket juxtaposition of menorah and Christmas tree, add a recent school board imbroglio in New Jersey and you have Mixed-Marriage Daughter--a mixed-up girl forced to make up her mind by the surfacing of small town anti-Semitism. In New York it didn't seem to matter that Sophie Barries was neither Gentil nor Jewish, especially at the Beardsley School for Girls; but in Woodview, Mass., there's no neutral ground at high school for the granddaughter of merchant Sam Golden, and no peace for half-a-Jew in Grandma Golden's kosher house. Intensifying Sophie's identity crisis is rich, attractive Ricky Taylor, who'd like her to lean the other way. And she probably would except for a certain discomfort and circumstance--Mrs. Taylor is leading the fight against the election of Uncle Harry Golden and another Jew to the school board. Still, it takes a tour of the lower East Side, talk with recluse refugee Great-uncle Joe (""Hitler made a Jew of me""), swastikas on the lawn, and an inspiring Passover Seder to show her ""the pain and pride of being an American Jew."" There are umpteen possible objections to this tract besides its title and the fact that it is a tract (""As if you could learn about being Jewish from a book""). Most are self-evident; one must be underscored--the author assumes the existence of widespread and virulent anti-Semitism (even among the ""Beardsley"" girls), disparages disaffiliation, counsels a united front and a fight. She does, however, raise some crucial questions.