Good move getting the Medistatin. Recently, I had a hen with serious sour crop. I treated her with that and sadly, she never improved. All you can do is treat and hope she's among the majority of chicken patients that will recover nicely with treatment. I had to euthanize my hen, and when I did a necropsy, I saw that it was cancer that had caused her yeast problem. Nothing was going to make her better.
Get a tube of miconazole at the pharmacy in the women's hygeine products. Start her treatment with that while you wait for the Medistatin. Be sure you treat twice a day for a full seven days.