It's not that driving is impossible, it's just impossible for a formerly-hoofed creature such as Sunset Shimmer. She had almost wrecked Flash's car in the past, and to be honest, it would've been funny if she did.

So without a ride to Pinkie's place, Sunset is forced to wait at the bus stop. She could complain about sitting in the freezing weather, or how the bus is notorious for being late and smelling like bodily fluids, but Adagio Dazzle is also waiting for the bus, sitting alone miserably on the bench and shivering in her boots.