Hell, the amount of 'stupid' advice I've seen people from the US give on here, I could say that EVERYONE from the US has no idea of how to look after their horse.
Back on topic. OP, yes molasses contains various vitamins/minerals, but the amount you have to feed for these to make a significant difference, will mean that your horse is getting far too much straight sugar in it's system among other things.
You are better off to look into various pre-mized supplements if you are that concerned about the vitamins/minerals in your horse's diet. There are fantastic supplements out there that cover all the different vitamins your horse needs in its system, rather than feeding molasses that has very few benefits.
As for coat shine, I feed sunflower oil and my horses have all gleamed on it. It's cheap, easy, and is also a great alternative to expensive hard feeds to fatten a horse up, there are more calories in just 1 cup of oil than there is in 1kg of many different types of feeds.
Even better than going for supplements, just make sure your horse has a balanced diet to begin with ;) Allow it access to plenty of good quality meadow hay, and work out a good feed mix that your horse responds well to.
If you want to be even more pedantic, get a blood test done on her to tell you what vitamins she is lacking in, and work from there, rather than just chucking anything and everything in it's feed because you've heard it's got some mineral or the other in it.
For the worming, don't mix the molasses with the wormer. What you can do is just coat the tip of the wormer, that goes in the horse's mouth, with molasses so horsey gets the taste of it ;)
Better still, try mixing a little bit of custard powder with water, and fill an old worming syringe with the mixture. 'Worm' her every day, or couple of days, with the custard mix in the lead up to worming her for real, so she expects a nice taste with the wormer ;)