Chicken injury? What is it?

One of my hens has a strange scab on her chest. Skin is a bit red, but not hot to the touch.

I poked the edges of the scab and some clear fluid came out from under it. When I poked it a bit more some white “grains” came out, in the fluid.

The middle of the wound has a deep looking hole beneath the scab.

My supposition is that this is a wound that scabbed over, but maybe had dirt or something it it?

Any ideas? How would you treat? Or leave it alone to finish healing?

Looks like an abscess. Isolate her, drain as much fluid as you can from it, and keep a close watch. If you're ok with giving her antibiotics, that would probably help too. But in general, keep the wound as clean as you can, and watch for signs that the infection might be spreading. Odds are, she'll pull through just fine :)

Howdy!
I have to agree with Ellendra Nauriel.
That looks like an abscess. I would clean the area, drain it, and keep it covered for a few days.
If it were my hen, I'd probably use some triple antibiotic or your favorite wound treatment protocol, then keep it covered as best possible. If it were deep enough to be concerning, I'd use "Wonder Dust" puffed into the hole - it may be under a different name, but it's a combination of activated charcoal and sulfa powder. It forms a great bond when mixed with any fluid. (Stuck a piece of my husband's thumb back on after a mishap with a mandolin; the slicer, not the musical instrument).

Other than that? Try to find out what happened. Interflock squabbles are usually the place to start, but she might have run afoul of anything pokey or sharp.
Good luck!

It is most likely an in-grown feather

I would open the wound and clean, then dab diatoms on the wound to dry out and create a new scab.

We figured it out. She, and a couple of other birds, are habitually roosting on a bar with their chests resting on a rough edge.

Fixed it.