Complex sentence: Guards!, she is a rather imposing Wagnerian aristocrat, but also a kind-hearted and compassionate person, embodying the positive aspects of aristocrats, who are otherwise depicted unflatteringly in Ankh-Morpork's population.
Split into simpler sentences: Guards!, she is a rather imposing Wagnerian aristocrat. Sybilis is a kind-hearted and compassionate person, embodying the positive aspects of aristocrats that are otherwise uncommonly depicted in Ankh-Morpork's population.