When a crop disorder isn't responding to treatment, there's a possibility that there's an underlying condition called pendulous crop. This is where the crop is badly supported and droops, not permitting the contents to empty.
This sets up the conditions for the contents to ferment and rot, thus the terrible odor. The contents can also become impacted, so you need oil and even a stool softener to loosen them up so they can be massaged out of the crop. But unless the crop is supported, the crop can't completely empty, which is necessary every 24 hours for good health.
You can determine if your hen may have pendulous crop by looking at her sideways and feeling the profile of her crop. Does it appear to hang lower than your other hens? Does it seem like a water balloon full of water, more teardrop shaped? Does it swing back and forth when she moves around?
When you massage her crop, try supporting it with one hand while you massage with the other. In theory you want to raise it up so the contents reach the level of the "drain". This way, you can safely empty her crop without vomiting her, which is unpleasant for her at the very least, and could cause her to aspirate the sour fluid into her lungs.
I would also give her a couple teaspoons of coconut oil to help break up any solid material and help the crop to empty. If she has pendulous crop, you will either need to manually massage the crop several times a day to get the contents to move through or you can fashion a "crop bra" for her out of elastic material to support the crop so it can empty on its own.
To treat and overcome the yeast infection, you need to treat twice a day for a full week. No skipping treatments, or it will only recolonize.
Your hen is slowly starving to death. Unless she has something else going on such as tumors, this can be successfully treated and she can return to good health. If she has pendulous crop, though, you will need to address that with a support device. I make one with an "H" design pattern. The legs of the "H" are 12 inch elastic straps, and the center is a 4 inch square scrap of thick material that will fit under the crop to support it. She won't be thrilled with it at first, but she'll quickly adjust.