She walked on her hands along the top of the wall.
Literal
She [topic-は] wall's top [object-を] handstanding walked.
逆立ちして歩く ('to walk while doing a handstand') — 逆立ち ('handstand,' literally 'standing upside-down') is used as an adverbial via the て-form. The path particle を marks 塀の上 as the surface traversed.