Fluid-filled lump under vent

[Bananabread]

This was taken last week. It's stayed the same and she's remained the same, soft and squishy

 

[Lillith37]

This was taken last week. It's stayed the same and she's remained the same, soft and squishy
View attachment 3708921

Looks very like what my girl had and what is not uncommon among laying hens. I wouldn’t worry so long as she is presenting well, with crop emptying and poop normal.