Cassidy was born to the Amell family estate, where she lived until she was nine years of age. At nine her magic manifested and she was sent to the Circle in Starkhaven. While there she focused on healing and spirit magic. She passed her Harrowing at twenty, after which she sought permission to assist in Starkhaven’s Chantry. During her work at the Chantry she met Sebastian Vael. Cassidy soon picked up a friendship with him after learning of his birthright, pushing him to reclaim his throne after his family was assassinated.

She gave birth to two children in the years following Sebastian’s crowning. The first child was a trap baby while the second was the spare to the heir. Cassidy cares more about appearances than the actual harmony of the family: luckily the children were raised by nannies. Despite owing her title and marriage to Divine Victoria’s ruling that the Mage Circles were to be disbanded, Cassidy believed in the sanctity of the Chantry over mages. She remains a devout follower of the Maker. Cassidy's first and foremost concerns are for herself. She retains a taste for the finer things in life from her childhood at the Amell estate.