Sour crop?

Hello all, some advice please...

One of my ex-batts, Queenie, didn't throw herself headlong out of the coop this morning when I opened the door.  She is very lethargic, drinking but not eating, and looking very sorry for herself.

I went out a little while ago to have a good look at her (thought I'd see if she perked up but she didn't).  I picked her up and the first thing I did was go to feel her crop, to see if it would give me any clues what was wrong.  She promptly threw up all over my feet (note to self: wear wellies in chicken run, not flip-flops!).  Watery green smelly stuff (sorry) with bits of grass and seeds in it.

Does this mean that what is wrong with her IS sour crop?  Or can throwing up mean any number of things?  She's still looking a bit hunched up and is drinking lots (taking the taste away?!).

I will get her some yoghurt later but should she really visit the vet?
 

Yes, saw the other thread but just didn't like to hijack it with my question 

I was trying to be gentle with her but I'd barely touched her before she just threw up.  I held her upside down for a while, stroking her throat and more came out.  She's now drinking lots.  I will see if she has any yoghurt later and how she is.  If no better, it'll be the vets first thing for her!  Luckily, I have a brilliant vet who's an avian expert so is great with the girls.

Many thanks for your help x