。
She can't ride a bicycle.
Literal
She [topic-は] bicycle [on-に] ride [thing-こと] [subject-が] cannot-do.
Japanese has two main ways to express ability: the morphological potential 乗れる, and the analytic ~ことができる (literally 'the act of X is possible'). Both translate to 'can ride.' The ~ことができる version is slightly more formal and explicit, often preferred in textbooks and formal writing; the morphological 乗れる feels more natural in everyday speech. Negated to ~ことができません ('cannot do'), the polite register is preserved.