。
She can't get by without a car.
Literal
She [topic-は] car [without-なしで] manage [nominalizer-こと] [subject-が] cannot-do.
~なしで済ます means 'to manage without' — 済ます (to make do, to get by) combined with なし (without). ことができない wraps the whole expression in a potential negative: she can't manage without a car. The sentence reveals a practical dependence — perhaps she lives in an area with poor public transportation.