。
She couldn't say a single word.
Literal
She [topic-は] one-word [emph-も] couldn't-utter.
発する ('to emit, utter, give off') is a vs-s-class irregular verb whose passive/potential is 発せられる; here 発せられなかった reads as the potential negative past — 'was not able to utter.' More elevated than 言えなかった ('couldn't say'); the choice fits dramatic or literary contexts where a character is rendered speechless by shock, grief, or fear. 一言も (ひとこともor いちごんも) + negative is the canonical 'not a single word' frame.