。
She was sitting in a chair watching TV.
Literal
She [topic-は] chair [in-に] sat [and-て] TV [object-を] was-watching.
椅子に座って + ~ていた frames a stationary, ongoing scene: the position is set, then the ongoing activity unfolds inside it. テレビ is one of the most thoroughly assimilated English loanwords — abbreviated from television, written exclusively in katakana, and treated grammatically like any other Japanese noun. テレビを見る ('watch TV') uses 見る ('look at, see') — Japanese doesn't distinguish 'watch' from 'see' the way English does.