。
She is very bad at driving.
Literal
She [topic-は] very driving [subject-が] bad-at.
へた is the negative pole of 上手 — the same XはYがZ frame, with the activity as the secondary subject and the skill rating as the predicate. Telling someone へた直接 to their face would be blunt; talking about your own driving you'd happily say 私は運転がへただ as a humble disclaimer. へた often sticks to hiragana even though 下手 has a kanji form.