When it comes to specific themes like that I always thing of embroidered blocks. I have done a couple of John Deere tractor themed quilts and are always very popular and make a lot of $$ out of them in raffles and auctions.
If you or her have an embroidery machine just get a few motifs and use them for the center of the blocks. They get so much attention that it doesn't require much around, just something simple with green and yellow.
Maria