Wood paneling

You can go with an unfinished paneling and stain or paint it with any color you want. Any stain will work as long as it's for wood. Then I would seal it with a good sealer to make it easy to wipe off when it gets dusty. I would probably stain it before putting it up, then do touch ups and lastly seal it. They have many water based sealers now that have little to no smell and are rather easy to use.

Is the natural one just "wood" or is there a finish over it? If it is "wood" then yes you can stain it--but--if it has a poly like finish on it--probably would not work well.

Have you shown her wainscoting? It's much more current and beautiful and you don't have to do the entire wall. You can buy the natural and stain any color, the directions for the stain are on the back of the tin. Just a suggestion, I'm not familiar with wood paneling but I would assume you would do a light sanding of the paneling and then put the stain on as directed from the manufacturer and use a polyurethane on top of that to give it nice luster. But that seems like a lot of work. Does she want to do the entire trailer in paneling or just a wall?

I googled "prefinished light colored paneling" and found this site. There are several she can look at.

https://www.google.com/search?q=light+colored+prefinished+paneling&rlz=1C1GGRV_enUS751US751&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwiKkrmV9aDaAhWBvVMKHTv9B4AQsAQI1gE&biw=1024&bih=690

Didn't there used to be kits that you could paint wood grains on walls? Then you can paint the background and the type of 'grain' she wants

How about looking for vinyl flooring in big width tile sections.

Super easy to paint sage