Whenever she goes out shopping, she ends up buying things she can't afford.
Literal
She [topic-は] shopping [to-に] go-out [whenever-と], [in the end-結局] not-fitting shopping [object-を] [end-up-doing-してしまう].
~に出かける ('go out to do ~') uses purposive に. 結局 ('after all, in the end') is a useful adverb for inevitable outcomes. 不相応 ('unsuitable, beyond one's means') is a な-adjective with a slightly bookish flavor — here it modifies 買い物 ('shopping') as 不相応な買い物 ('shopping beyond her means'). The closing ~してしまう adds the regret-tinged sense of 'end up doing.'