When you do a portrait session for someone and don't know what size print they will want it's a good idea to use "non-destructive" cropping:

MAKE A DUPLICATE LAYER. Choose the dimensions you want in the Tool Options Bar over the image (they're not shown here because once you draw the crop box that Options Bar doesn't show, but the "Hide" box does).

Put a check mark in the "Hide" box (won't show unless you're on the second layer).

Save your image as a PSD.

Next time you use that file you will be able to recrop because you've retained the cropped off part.