。
She can't help but laugh.
Literal
She [topic-は] laugh cannot-help-but.
~ざるを得ない is a formal, literary double-negative construction meaning 'have no choice but to, cannot help but.' Built from the classical negative ~ず (attributive form ざる) + を得ない ('cannot obtain [not doing it]'). Despite its formal grammar, it's used in everyday speech for situations where an action feels inevitable or unavoidable.