Lark is an ambient thread mage with powers in spinning, weaving and other manipulations of thread. She shares Lady Sandrilene fa Toren's magic, and becomes her permanent teacher in threadcraft and magic throughout the Circle of Magic series, beginning by teaching Sandry to spin early in Sandry's Book. After Sandry becomes fully accredited as a mage in her own right, the two remain close friends, and she gives Sandry advice on how to deal with the girl's first student in Magic Steps.
Unusually for a mage, Lark did not discover her magic until she was thirty, not realising until then that her interest and talents with thread were magic. Despite this, Lark is now considered a Great Mage, one of the most powerful thread mages living - though even she cannot manipulate pure magic as her former student Sandry can. Before discovering her magic, Lark lived for many years as a tumbler, travelling all over the fictional world of the series. Some time before she discovered her magic, however, she became sick with asthma and was no longer able to work. She was forced to live in the slums of Emelan's capital Summersea, because she could not afford to live anywhere else.
Lark is said in the books to have glossy dark brown hair and cocoa colored skin; she is also cheerful and good-natured, in direct contrast to Rosethorn, who is prickly and sharp tempered. Throughout the series, Lark is the one the characters turn to for advice or comfort. Although she shares Discipline Cottage with Rosethorn throughout the series, and the two are always described as being the best of friends, the truth of their relationship is not revealed until The Will of the Empress. While Rosethorn is described as bisexual, the details of Lark's sexuality beyond her relationship with Rosethorn were not elaborated upon.