ive used milk paint from general finishes over poplar with no priming it took 2 coats.
If you go the milk paint route, I would suggest a clear top coat of some sort.
or you could go with spray cans of your final color
FYI, the General Finishes "Milk Paint" isn't milk paint. It is a water based acrylic.
MSDS sheet: http://www.generalfinishes.com/msds-dat ... 282%29.pdf
(hint, contains no casein). The powdered stuff from other sources is the real deal. Or you can make it yourself from scratch.
However it is correct that a milk paint needs a protective top-coat. The real stuff, while pretty tough, is not waterproof and will be quite flat. Oil, wax, poly all work as top coats and work to deepen the color and create various levels of sheen and gloss.
I painted my Shaker cupboard with milk paint and the darker color (brick) had better coverage than the lighter color (mustard). But because it is water based it raised the grain so consider pre-raising the grain and sanding back and sanding lightly between coats. Also, because of the water content, it swelled the wood and what was a well fit door suddenly wouldn't close. It has since relaxed and closes properly but it took a couple weeks.
It could be she is thinking of ebonized (or at least furniture that looks like it has been ebonized) for the black color. I think you can do that with poplar but I doubt poplar has enough tannic acid for the simple vinegar+steel wool trick to work. The commercial stuff is probably a recipe of glazes and stains.