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.