On the grit, they still need it. It's been shown that birds who have grit available use all their food more efficiently. They need grit-sized grit, and it needs to be a certain hardness so it stays there in the gizzard til it's all ground down to nothing. Lime rocks won't do this, oyster shells won't do it. So buying a small bag of granite grit (or the very nice mineralized or pigeon grit) will really help them.
I like it as an insurance policy against slow crops. A little money spent on grit (it's very inexpensive to buy the little pretty bags from CalfManna) will be repaid to you back in weight gain and feed use.
If you get chick grit, it smells lovely - of anise (licorice) and is mineralized (red) and attractive. If you get the adult grit, it's grey. Mine like the red better - like mineralized (iodinized) or pigeon grit.
On the mash, see if you can use her pellets crushed in the blender as at least part of the base for the nutrients. If she won't eat it, try whichever she will eat.
The solidification of the droppings is a nice sign. And yes- do give by beak (carefully) any nutrients you can to keep her up. You can make a thich 'broth' out of crumbles, yogurt, the vitamin water and a tiny bit of honey to get her to 'drink' more nutrition if you have to. Do give the vitamins at least in the beak so you know she gets it.
On A, it's safer to give polyvisol than straight A. If you do straight A, betacarotene oil capsules are a little more safe than straight A as the body will make A from betacarotene in the amounts it needs.
I also agree that keeping her from the continued heat strain is very good. Hopefully if you just keep going, she'll improve. Looks to be slowly but at least improve.
And yes - don't worm. She's too weak kfor it.