Yes! Vitamin A comes with Vitamin D in it. Sometimes it also comes with Vitamin E. These are the fat soluble Vitamins so are frequently packaged together.
Here is a link to an injectable iron available from Valley Vet. We but a lot of supplies through the mail from Valley Vet and Jeffers Livestock Supply. They also have the Vitamin A. Ferrodex 100 Agri-labs (Farm Supplies - Swine Health - Swine Iron).
Like I think I mentioned, baby pigs get anemia if they are not raised on dirt, so they are just routinely given an iron injection. This stuff orally really gets a quick pick-up going on malnourished horses. None of these items are going to hurt a horse whether they need them or not and it appears that yours really needs them.
If she is starting to pick at the grain, that is good. Just limit her hay and she will eat more of it and give her the Vitamins and Probiotics to 'jump-start her.
Please do not de-worm her again without a fecal showing that she needs it. Zimecterin Gold is a very harsh de-wormer, but it is also very effective. A good probiotic (or fresh 'clean' manure) will help get her gut back in shape after the de-wormer. I would have a fecal done in 60 days or would just go out and de-worm her with a mild de-wormer like Safe-guard or Anthelcide. I would follow up in 30 to 60 days with an Ivermectin de-wormer to get the Bots.
It is perfectly normal for horses to have Bot eggs on them this time of year. All of mine do. The bots have not started migrating yet and are not available to a de-wormer until much later in the year. If you remove the eggs, those will not migrate, but you will never get them all and will still have to de-worm for them in the winter and again in the early spring.
I know what you mean about Vets. I thought you were probably dealing with a country Vet. I used to live in the mountains of Colorado and the nearest good equine vet was 75 or 85 miles away and over a mountain pass, so I lived with the all-purpose Vet clinic and learned to do most things myself. When I moved from there, the local Vet were sending me all of their bad 're-hab' cases because they did not want to bother with them and could not make enough money on them. "Necessity is the mother of invention!" It is also the mother of learning to do it yourself.