Heinlein's wife in question was his second one, and her maiden name was Leslyn Macdonald. They were married in 1932 and divorced in 1948. During their marriage, and possibly even a little earlier, she called herself a Witch and called her magic Witchcraft. But from what we can tell at this remove, she wasn't even remotely Wiccan in the Gardnerian sense, much less initiated into Gardnerian Wicca. To the extent that the Witch in Heinlein's novel Magic, Inc. is built on Leslyn's Witchhcraft, it was derived partly from the esotericism of the variant form of the Theosophical Society then current in California (of which her mother had been a member), and in large part from Grillot de Givry's Witchcraft, Magic and Alchemy.