Hello there and welcome to BYC!!
I am sorry you are having trouble with your bird. Read this article I wrote on Crops and the issues birds can have with them. It may help you to understand how crops become slow, sour or impacted. http://www.backyardchickens.com/a/impacted-slow-and-sour-crops-prevention-and-treatments
As for giving her medication, did the vet give you Nystatin? This medication is not all that useful on a crop with any food in it. The meds need direct contact with the yeast infection unfortunately. So make sure to give this to her first thing in the morning if her crop is empty or after she is vomited. (I have given instructions on how to vomit the bird without aspirating them. Follow them very closely) Then don't let her eat for an hour or so until the meds soak through the yeast infection.
If you are syringing liquid down the beak, only use a 1/4 or 1/2 ml at a time and syringe, without the needle, on the lower mandible, (beak), in front under the tongue. This is a very small amount and will not aspirate them. As soon as you slowly squeeze the liquid in, close the beak and rub under the chin. She will swallow.
You can also put liquid meds in baby food. Baby food is thick and you can put in 1/2 to 1 ml at a time under or on the tongue.
Pill like meds can be broken up and put in raisins.
Do not let her free range until this is cleared up. No hard grains or seeds. Dampen her layer feed. Chickens love damp food and she will eat more readily. If she is not eating much, feed her what ever she will eat, as long as it is water soluble. You want to keep the crop moving as fast as possible.
Keep us posted and I hope she makes a full recovery! :-)