。
She had to give a speech in front of a large audience.
Literal
She [topic-は] a-lot [genitive-の] audience [genitive-の] front [at-で] speech [object-を] do [had to-なければならなかった].
聴衆 (chōshū, 'audience, listeners') is the formal Sino-Japanese word for an audience of listeners — distinct from 観客 ('viewers, spectators') used for visual performances and 読者 ('readers'). The で after 前 marks the location where the action happens. The full obligation pattern ~しなければならなかった ('had to do') stacks the negative conditional ~しなければ ('if not') with ならなかった ('it wouldn't do, was no good') — a double-negative structure that adds up to 'must.' Note the alternative casual form ~しなきゃ・~しなくちゃ contracts the same construction. 話しをする (note: typo for 話をする, meaning 'give a talk/speech'); 話 by itself is the noun.