Hmmm ... his lady friend is the one interested, and she doesn't like plastic ... American Holly, properly finished in a shiny CA finish after buffing, would probably look like a white or off-white plastic.
I might think about asking her if she has a particular preference for the wood species, especially if she wants to see wood grain. Beech, Maple, Poplar, and Persimmon (white ebony) come to mind.
Also, if the grain interference might be a problem, you could also mention that there's a white background decal paper you could use, in addition to the clear background paper. In fact, you could possibly make one part of the design using clear, so that you can see the wood grain through it, and the part that needs to show up clearly could be made on white background paper.