。
She had such a bad cold that she couldn't get out of bed.
Literal
She [topic-は] terrible cold [because of-で] bed [object-を] leave [can-ことができる] couldn't.
床 here reads とこ, not ゆか — same kanji, two readings, very different meanings. ゆか is the architectural floor; とこ is one's sickbed or sleeping place, surviving in expressions like 床に就く ('go to bed, retire for the night') and 床を離れる ('leave one's bed, get up'). The ambiguity is one of those cases where context entirely picks the reading. を marks 床 as the point being departed from — one of を's less common uses, attaching to verbs of leaving (出る, 離れる, 卒業する).