I agree with using a measuring cup BUT please know that a household measuring cup is LIQUID measure. If you feed dry matter according to liquid markings on the cup, you will be feeding a lot less than one pound, ask me how I learned that one
Meaning 8 ounces of liquid is not the same weight as 8 ounces of dry matter.
Buy either a fish scale or a dry weight scale at WalMart.
I feed a Senior feed and rice bran to my hard keeper and imagine my surprise when I weighed them and there's a lot more difference in the quantity of a pound of Senior feed vs. the rice bran
I can tell you what my vet told me with my very hard keeping 27+ Arab, who is only 13.3H. "double up on everything you're currently feeding".
The vet had done a CBC, checked his insulin & cortisol levels, teeth, examined him for possible tumors, did fecals.
The verdict was he is healthier than I am and has the metabolism I wish I had
Since your horse hasn't been getting much of anything, I would start out slow -- if you can manage to feed three times daily that would help a lot. Twice a day for sure, given the condition she is in --- shame on them
Again, keep in mind the Arab is only 13.3H and the vet was full aware of this amount:
1. Nutrena Safe Choice Senior; he was going thru a 50lb bag every 14 days but I have recently cut him back to where 50 lbs now lasts 19 days.
2. Pelleted rice bran; he was going thru 60 pounds a month but I've recently cut him back to 30 pounds a month.
3. Timothy pellets 30 pounds a month and he's still eating that amount.
4. Well soaked timothy/alfalfa cubes (he has four missing molars) 90 pounds a month after soaking.
5. Ten pounds of orchard grass/mix hay at night; he's on 20+ acres of pasture during the day. He won't eat all his hay which is why I feed so much bagged forage.
In 54 years of paying for my own horses, I have never had to feed a horse that much, especially a little guy like him.
Once you get your horse on a steady feed program and she starts to gain weight, you can start increasing her feed pan stuff. Looking at her and assuming she will gain weight in a normal manner, you should see her pretty much back to normal in three months - four at the most and by shedding season, she will be a beauty once again
Just don't forget to buy yourself a dry measure scale because those ounce marks on household measuring cups are liquid measure
Best of luck getting her back to good weight