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She's got this whole big room all to herself.
Literal
She [topic-は] this big room [object-を] all [alone-monopolize-独り占め] is-doing.
独り占め ('monopolizing, having all to oneself') is a vivid native compound: 独り ('alone, by oneself') + 占め (verb stem of 占める, 'to occupy, take up, hold'). The ~を~する frame makes it transitive: 部屋を独り占めする ('monopolize the room'). Often used somewhat enviously or critically, with a hint that the speaker thinks the resource is being hogged. 全部 here is an adverbial 'entirely, all,' modifying 独り占め — 'monopolizing it ALL.' The whole sentence has a slightly playful or grumbling tone, the kind of remark you'd hear from a sibling, roommate, or coworker.