。
She bent down and picked up a pebble.
Literal
She [topic-は] body [object-を] stooped [then-て] pebble [object-を] picked-up.
身をかがめる ('to stoop, to bend one's body down') is a set expression where 身 ('body') is the direct object. The compound verb 拾い上げる joins 拾う ('pick up from the ground') with 上げる ('raise'), emphasizing the upward motion of retrieval. This ~上げる complement is productive: 持ち上げる ('lift up'), 引き上げる ('pull up'), 見上げる ('look up at').