。
She called for help, but nobody came.
Literal
She [topic-は] help [object-を] sought [but-が] nobody came-not.
The clause-final が (but) creates a stark contrast between the desperate action and its futile result. 誰も来なかった uses the pattern 誰も + negative verb = 'nobody did X.' The tension between calling for help and receiving none makes this structurally simple but emotionally effective.