。
Last night, Yumi was the one who came on to me.
Literal
Last-night [topic-は] Yumi [genitive-の] direction [from-から] challenged-came [explanatory-んだ].
A relationship context sentence with a defensive tone. ほうから ('from the direction of / from X's side') emphasizes that the initiative came from Yumi, not the speaker. 挑む (いどむ, 'to challenge / to make advances') is a strong verb — here suggesting romantic or sexual initiative. ~てきた adds directionality: the action came toward the speaker. んだ (= のだ) at the end is explanatory — the speaker is justifying or explaining the situation.