Very often, DIY finishing is as much a job as actually making a piece of furniture.

There are no magic finishes, despite what the ads say.

The best way to accomplish what she wants with just adding a layer of finish is to try garnet or seedlac shellac. But, you need some experience in choosing and using it.

Here is a link that might be useful: Shellac supplies

Not to offend the woodworkers :) but this might be a case for something like Minwax Polyshades. It's like tinted poly (maybe it IS tinted poly?). It'll obscure the grain a bit but it's not that bad (assuming you're not doing this to a lovely antique). It'll at least be a washable finish which isn't always bad when you're dealing with poop.

Yes, there are two ways.

1. A toner. This is finish with color in it. To be successful, it almost has to be sprayed and it has to go on lightly. Goes from not quite to too much real quickly. Technically, Polyshades is a toner, though it is miserable stuff. A friend calls it the worst thing to happen to a can. In addition, poly does not stick all that well to lacquer, the most common commercial finish. You can get lacquer-based aerosol toners from places that cater to professional finishers and touch up techs. Mohawk is the most common brand.

2. Glaze. A glaze is a heavy on pigment, light on binder colorant that you apply between layers of finish. You must top coat it with a clear coat. I often use glazes to adjust colors in the finishing process (a little darker, a little more/less red, etc.). I also use glazes as "hang up glazes" to give an overall highlight and darken crevices, making the piece appear not "sparkling new." I make or buy glazes, but some people use gel stains as a glaze substitute. It's also important to not go too heavy with a glaze because besides muddying up, too thick a layer can cause adhesion problems.

I use both of these products to kick colors in certain directions.

For a more thorough discussion, with photos, see Bob Flexner's "Understanding Wood Finishing" (2d ed.) and/or Jeff Jewitt's "Complete Illustrated Guide to Wood Finishing."

General Finishes brand Gel stain .... marvelous stuff!

You just have to thoroughly clean the piece with mineral spirits and steel wool, then wipe on the glaze with a soft cloth, and then a coat of their gel topcoat. it's oil-based, but not horribly stinky.

http://www.highlandwoodworking.com/generalfinshesoilbasedgelstainscolorchart.aspx