、。
She wants to buy a car, but she can't afford one.
Literal
She [topic-は] car [object-を] want-to-buy [explanatory-のですが], buy ability [subject-が] not-exist [explanatory-のです].
~のですが (explanatory + but) sets up the first half as background: she wants a car. The が softly transitions to the problem: 買う余裕がない (no room/means to buy). 余裕 (よゆう) means margin, leeway, or affordability — 余裕がない is the standard expression for 'can't afford.' The double のです (beginning and end) creates a fully explanatory frame, as if the speaker is laying out a situation.