。
She's going to be on TV tonight.
Literal
She [topic-は] tonight TV [on-に] appears.
テレビに出る ('appear on TV') is a fixed collocation — the particle is に, not で. The same に marks where a person 'comes out into,' parallel to 舞台に出る ('appear on stage') or 試合に出る ('compete in a match'). テレビ itself is one of the oldest and most established katakana loanwords, fully naturalized: it forms compounds (テレビ番組, テレビ局) and verbs (テレビに出る, テレビを見る) just like a native noun.