She had used her victims’ blood for bathing, in the hopes that it would help her stay young and beautiful. She dies a few years short of turning 200 years old (FW).
196 years is a long time to live - even for witches and wizards. Vampires are generally understood to be functionally immortal, so it can be inferred that Lady Carmilla Sanguina's time as a vampire is counts as part of her life and that her death occurs when her vampire self is destroyed. -BB