In Sarah Littman's book, Confessions of a Closet Catholic, Littman (a Reform Jewish woman) writes a tale of a Jewish girl who decides to give up Judaism for Lent and practice Catholicism. She takes Communion with matzos and grape juice and confesses to her teddy bear "priest". Then, her very Jewish grandmother dies, which makes her question whether it's God's punishment and whether she should return to Judaism. The author does say in an interview that her character resembles her teenage self in a spiritual-seeker sort of way.
What is the truth behind this story? Is it really spiritually dangerous to practice Christianity? Since idolatry is forbidden in Judaism, what are the spiritual and earthly consequences?