Complex sentence: Her mother left the Church when she was eight, but remained interested in spirituality, while Maggie became an atheist and a follower of Ayn Rand and, to a lesser extent, Robert A. Heinlein.
Split into simpler sentences: Her mother left the Church when she was eight, but remained interested in spirituality. Maggie Gallagher herself moved toward an atheism influenced by Ayn Rand and, to a lesser extent, Robert A. Heinlein.