If your mom is sponsoring the pills, go for them lol, but you'd need a lot to see any results.
Easy to see when you compare human weight to horse weight lol.
Maybe you should re think the feeding, if she's usually an airfern, but needs Healthy Edge in winter to keep it on. I'd rather get an extra bale of hay or two if BO doesn't supply enough than giving her sweetfeed( there are worse feeds than healthy edge, but still). Then get her either one of the vit/ mins I mentioned earlier, find flaxseed, maybe have a look at the Yellow Pages for a feed mill or country store somewhere near and call and ask. If you feed 1/4 lb a day, 50 lbs flax lasts a year and more.Helping her getting rid of the winter hair is a good idea. That old stuff is itchy.