First, stop giving her water; she's not able to get it into her body, thus the full, water-balloon like crop you're feeling. Two things that come to mind to me (maybe 3), aside from disease, are Impacted Crop, Eggbound, or Worms (maybe).
A few questions:
How old is the pullet?
Has she laid any eggs yet?
What does her diet consist of?
When did she last eat?
Does she free-range?
If so, what does she eat free-ranging?
What kind of treats does she get, how often?
Has she been treated for intestinal parasites (worms)?
Has she been treated for any other illnesses?
Below is a good explanation of Crop Issues with a guide to how to treat Impacted Crop. In short, you're going to give her some oil orally so that it helps lubricate the blockage. You're also going to massage the crop in a top to bottom motion with your fingers to try to encourage the blockage to move. Also massage the sides of the crop with gentle but firm massages between your index finger and thumb.
For oil, some use Vegetable Oil, others Olive Oil, still others Coconut Oil. Any will work, but the Coconut Oil can be frozen and small bits broken off to more easily get into the bird. For the others, you're going to need a syringe or dropper to give her the fluid. Collect the dropper/syringe, then read the link below.
https://thegreenestacre.com/impacted-crop-signs-and-how-to-treat/
We can cover being Eggbound once we know her age and laying history.
Last, Worms can cause an intestinal blockage if she's overly infested with them. Her age will give us a clue to the possibility of that. Also, look closely at her stool to see if you see ANY Worms.