A "separate shower" means that the shower area is not connected or combined with other parts of the bathroom. It is a stand-alone space specifically designed for taking showers. Full definition
Total luxury fills the elegant open living area, one bedroom with a private terrace and bathroom with separate shower stall and an oversized bathtub. (krabi-hotels.com)
They had separate shower rooms for guys and ladies. (boundfortwo.com)
Their oversized bathrooms feature separate shower and tub and marble floor. (travellermade.com)