The moment Yuka was introduced to the new English teacher, she fell in love.
Literal
Yuka [topic-は] new-appointment-of English-of teacher [to-に] introduce-[passive-された]-moment, love [into-に] fall-[past-た].
~たとたん ('the moment X, as soon as X') is a vivid narrative marker for sudden or surprising sequences. Combined with the passive of 紹介する ('introduce'), we get 'the moment she was introduced.' 恋に落ちる ('to fall in love') is the Japanese idiom, identical in imagery to English. 新任 ('newly appointed') is formal/professional vocabulary.