。
She cried out for help.
Literal
She [topic-は] loud-voice [with-で] help [object-を] sought.
大声で is the instrumental で ('with, by means of') — 'with a loud voice.' Combined with 求める ('seek, request, demand'), the result is 'call out for help.' 助け is the noun form of 助ける ('to help, save'); 助けを求める is the most direct 'cry for help' phrasing. Note that Japanese uses 求める specifically for actively seeking or demanding something — softer 'ask' words like 頼む or お願いする would shift the tone.