。
She wants a cat.
Literal
She [topic-は] cat [object-を] [is-wanting-to-keep-飼いたがっている].
~たがる is the third-person desire suffix — derived from ~たい via ~がる. Where ~たい is for the speaker's desire, ~たがる describes another person's outwardly visible desire (since you can't directly observe their mind). Combined with ~ている for ongoing state.