Complex sentence: While it is not known what ever became of Calla's mother, as there is never any mention of her mother in any of the episodes, it is often assumed by fans that Calla's mother died before the series timeline.
Split into simpler sentences: While it is not known what ever became of Calla's mother. As there is never any mention of her mother in any of the episodes, it is often assumed by fans that Calla's mother died before the series timeline.