What happens to Victor’s mother?

Victor's mother comes down with scarlet fever while caring for Elizabeth. Unlike Elizabeth, she doesn't survive the illness.

Elizabeth was saved, but the consequences of this imprudence were fatal to her preserver. On the third day my mother sickened; her fever was accompanied by the most alarming symptoms, and the looks of her medical attendants prognosticated the worst event.

She died calmly; and her countenance expressed affection even in death.