She [topic-は] screaming [while-ながら], knife [object-を] brandished.
叫びながら ('while screaming') sets simultaneous action. 振り回す (ふりまわす, 'to swing/brandish around') is a compound verb: 振る ('to swing') + 回す ('to go around'). ました is the polite past. A dramatic, violent scene rendered in clean, direct grammar.