Well I'm not going to join in on the health crazed debate here, but will just say that I would think that the amounts of vit./mineral in the molasses is probably fairly minimal, so feeding it every other day, most likely won't do much good. If she needs more minerals, I would strongly suggest getting a free choice mineral that you can put in her paddock with her. If you are feeding the molasses in order to get her to eat something, I honestly see nothing wrong with it...especially if she is getting such a small amount. Just moniter how she acts on it, and if she seems out of sorts, or hyped up, you may want to cut it out.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."