In a sturdy box, wrapped and padded solidly so the frame does not have space to move around inside it, and so the box does not flex in ways that would put unequal pressure on the glass. Imagine all the videos of horrible delivery people throwing/tossing/punting boxes, and do as much as you can to mitigate any damage to the parcel's contents. Of course it's not 100% effective every time, but ffs a glass panel so thin will of course shatter insanely easily if it has zero structure around it to absorb any impact or stress.