Supplement Suggestions

Soaked beet pulp and soaked hay cubes should work. You will need to weigh her feed. Weigh everything dry if you do soak..( you should soak beet pulp)
She should get 1.5 to 2% of her body weight in feed per day.Mostly Hay...
Most people feed in at least to feedings. So if she is 1000lbs she needs to be eating 15 to 20 lbs of food per day.
If she is old, try adding a senior ration. You can wet that to, if she has trouble chewing.

Sorry edit: 15 to 20 pounds if she is 1000 pounds and up it if need be.

Put the horse down!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!1 Jeezuz! Bit extreme don't ya think. If the horse is happy then never dismiss its life.

Yer ... I was giving her like 4 biscuits per day until I found out she had hardly any teeth.. thanx dad for wasting your money on hay.

If the horse does not have teeth or hardly any teeth she needs to be fed a mash several times per day if she cannot eat and digest hay. She will need to eat at least 20lbs per day of hay cubes or pellets made into a mash, possibly more if she is now underweight. It's not a good idea to feed more than 5lbs per feeding so that's at least 4 feedings per day. If that is not possible then the quality of life of the animal starts to suffer. It would not be in anyones best interest to rehome the animal with this condition so it might be time to look at putting the horse down, especially if she cannot maintain proper weight. I'm not saying it to be mean but these things do need to be taken into consideration.

What has the vet said about this horses condition and feed program? By the way if the horse cannot eat hay and is not getting fed enough feed that it can eat so it is losing weight I wouldn't call that a happy horse but rather a hungry horse.

OP.......can she still eat at least some hay, does she nibble on it?
If so, leaving hay in front of her is a must. It should be soft hay, not the stemmy, stalky stuff. Alfalfa hay would be good, the little leaves are soft and it has more calories than normal hay.
Then senior feed was mentioned. Some, not all, senior feeds can be fed alone, without hay, are already soft to chew or can be soaked( in general, pouring some water over it and the pellets fall apart within 10 minutes or so).
So giving her soft hay or alfalfa, and for real nutrition a good senior feed as often as possible spread out over the day, like early morning, again at lunch, early afternoon and the last one just before you go to bed, should do the trick.
I also agree with soaked alfalfa pellets if she can't more than suck on normal hay. Again, soaked and several times a day.

Yer she does try eating the hay, I think she can chew some of it and then spits wad out. She can eat carrots fairly well.

Please take into consideration that horses need to be fed little and often, and by only one or two larger meals per day you are harming the health of her digestive system and risking with colic. You should really put an effort in splitting her feeding into many smaller meals, if you care to have her around healthy and happy for a while at least.

Soaked sunflower meal is a great source of good quality proteins, if you can get it around where you live.

Okay, then go the senior feed way, get the complete kind, which you can feed alone. Give her the recommended amount for her weight, divided into AS MANY MEALS POSSIBLE, as I described above and hay in front of her all the time, she will nibble enough of it to prevent her stomach acid from eating up her stomach and the senior will give her calories