I [topic-は] met [instant-瞬間] her [object-を] liked-became.
会った瞬間 ('the moment I met her') — 瞬間 (しゅんかん, 'instant, moment') functions like とたんに but as a noun. 好きになった ('came to like') uses ~になる with 好き for falling in love. The lack of particle after 瞬間 is natural — time nouns often appear without に.