Bertvee, these are my thoughts, though keep in mind that I am by no means an art expert, nor an expert on Godward.
It's clearly a copy, and in my opinion an "average" one. Godward sets a very high standard with his shadows and materials. Look at the face on the original, then at the copy. Look at the perspective with the floor tiles in the original, and then look at the trouble the artist had getting it right in the copy. I like the copy, but it suffers in comparison to the grace of the original.
My guess for shifting the image is that the copyist wanted to put the figure into the centre. Godward is using the "rule of thirds," which I think makes for an interesting composition. The copyist wanted the woman in the middle, which feels slightly unbalanced to me.
Read here about the rule of thirds.
I think the one you have is lovely, and it may be worth some money (I don't know). I just wouldn't hang it right beside the original. ;-)
I hope that helps,