It does sound as though she might be an internal layer. She is leaking yellowish from her vent? That could be egg yolk from an egg that broke before she could move it down and lay it. The crop could be sour as well. I would go with the suggestions that have already been made. After the bath, you can put on a glove, and lube your finger, and very carefully do an exam though her vent. It might tell you if anything is in there.
You also might want to gently massage her crop. Gentle massage may help to move things through, and it may also help to tell you if she has a ball of fibrous grass, etc. in there or if it is just fluid. You can also enter sour crop into the search feature, and it will bring up threads that may have helpful information.
Good luck with your girl.