Sick Chicken

if she sounds gurgly is she also sneezing and does she have any bubbles in her eyes, any facial swelling? Open her beak and have a sniff.
She could have mycoplasma in which case your vet will need to prescribe a broad based antibiotic such as Aureomycin, Tylan, Denagard or Baytril and you will need to get enough for all the chickens.
Chickens can have this from before they are hatched as it can be passed down from the hen to the chick when the egg is still inside her (if they have it you should never breed from them) and any stress such as new home, moulting etc can trigger an attack. You will never get rid of it but you can usually control it.

the fluid could have been a sign of sour crop or impacted crop. If the others are showing no signs then don't worry but just keep a close eye on them for the next couple of weeks. If they show signs of the same thing then go back to the person you bought them off