Would it be so horrible to say that you would like something else rather than art work.
"Oh, Mom. Really it is sweet to think of getting us some art work, but the new place IS much smaller than what you probably are thinking. We already have items for the available space and are figuring out that we don't have room for so much. But you know what I would LOVE and would be so grateful to have is a new toaster (or whatever other small item that would make your life easier). We actually were looking at these two models (make sure that they are small enough and different price points)."
I just Googled Toaster Retro look and got a few hits. Even some come in SW colors.
*For her issues about there is No Way that your place can be smaller than hers. Can you give her an example of "well, our living room/lounge is about the size of the second spare room at Grandma's."?
I have had that problem with my office. When folks hit a certain anniversary years, the company gives a gift. When I hit 10 years, most people were getting artwork (pictures, sculptures) And I created a stir because what I wanted was a food processor. I got it but there were some FREAKED out people because of it. (Now they just give gift cards)