All from references. Study. But in some cases things might be changed, like another dress or other things. On different refs I like different things, on some special poses, on some light, placement of hands, skin glance ect. ect.
face itself
beautiful light from bottom
hand position
cute knee legs position
general pose
hands position
here was cool glance on a spine, but becaue I've tested catroon shading balance I removed it at final (otherwise it start looks more real)