。
Did she show you that photo?
Literal
She [topic-は] you [to-に] that photo [object-を] showed [question-か]?
見せる ('to show') is the lexical transitive of 見る ('to see') — note that Japanese has dedicated transitive verbs for 'show, let see' rather than relying on a causative form, although the causative 見させる also exists with a slightly different nuance (forcing rather than offering). The pattern XがYにZを見せる ('X shows Z to Y') keeps to the standard double-object frame with に for the recipient and を for the thing shown.