There is indisputable evidence that preChristian Jews believed in a Hebrew Goddess.  (See, e.g., The Hebrew Goddess, by Prof. Raphael Patai; Did God Have a Wife", Prof. Wm. Dever).  Princeton Prof. Elaine Pagels convincingly demonstrates with many citations, that early Christians also believed in a Mother in Heaven.  Some early Christians believed in a different sort of trinity or triune God:  Heaven Father, Heavenly Mother and Jesus the Savior.  Thus we see, the idea of a Heavenly Mother, found in belief of The Church of Jesus Christ of Latter-day Saints, is not unusual at all.