Elizabeth Lavenza – Wikipedia

Role in the novel. Born in Italy to an Italian nobleman and a German woman, Elizabeth Lavenza was adopted by Victor’s family during a stay on Lake Como, after her parents’ death.While Victor’s cousin in the original 1818 release of the novel, in Shelley’s 1831 rewrite she is first introduced as Victor Frankenstein’s unrelated, adopted sister.

Link: https://en.wikipedia.org/wiki/Elizabeth_Lavenza