。
She got upset at his remark about her bad driving.
Literal
She [topic-は] driving [subject-が] bad-at thing [about-について] [genitive-の] his words [at-に] stomach raised.
腹を立てる ('to get angry,' literally 'to raise one's stomach') is one of many Japanese body-part idioms tied to emotion — the abdominal area is associated with deep, gut-level feeling rather than the chest or head. The に before 腹を立てる marks the trigger of the anger: she's angry at his words. The pre-modifier chain is impressive: 運転が下手な事についての彼の言葉 — '[her] driving is bad' (clause) → '事' (nominalizing 'fact that') → 'について' ('about') → 'の' (genitive-attributive) → '彼の言葉' ('his words') = 'his words about the fact that her driving is bad.' Five layers of modification onto one noun, perfectly normal in Japanese.