Between late October and early November, 220 BC she was married to her brother, Ptolemy IV. They ruled jointly for sixteen years. In Summer, 204 BC she was murdered in a palace coup, shortly before her husband's own death.
External link A more detailed profile of her, in a site devoted to her dynastie:http://www.geocities.com/christopherjbennett/ptolemies/arsinoe_iii.htm