I would always make water available for her during waking hours.
You can give her yogurt for probiotics, that's fine - about 1 tablespoon a day.
Withholding food for a day may help during treatment.
Can you get an over the counter vaginal yeast or anti-fungal cream that contains Miconazole or Clortrimazole? That is what I would use to treat the sour crop. Instructions are in the link below but I just draw up the correct amount of cream and direct dose the hen twice a day.
Don't massage the crop if it's sour.
With her being an older hen the crop issue may be due to a reproductive disorder or other underlying condition, but hopefully you can get it cleared up to make her more comfortable.
Offering her a little wet mushy feed or bits of soft cooked egg is fine if she's willing to eat.
I recommend that you read the whole article, it has some good information. Get back with us on how she's doing.
https://www.backyardchickens.com/ar...w-to-know-which-one-youre-dealing-with.73607/