It’s really uncommon to see non-plant-stuff here, but I’ll try to help you.

My first reaction was “Go to the vet”, but I think, as harsh as it sounds, for the cost of one visit you can buy 100 more egg-laying dinosaurs… So, this only an option if the chicken has a big emotional value to you.

I think the best option is to buy both a desinfecting, and then use a wound-healing ointment, both from the pharmacy.
For disinfecting stuff, you can buy something based on iodine or silver for example. Do not use alcohol or stuff like that!
And for wound healing, you can use something based on panthenol, with a neutral carrier.

Keep her out of the sun, and treat + check her multiple times daily.

If that still doesn’t help, consider antibiotics from the vet, but that will be way more expensive.

Isolation with separate food/water for a little bit is a good idea. Other hens will peck at wounds. I’d observe behavior to see if she’s sneezing or any other indication of sickness.

Sometimes other birds will peck at a wound on one hen, so separate this bird from the others for a few days. Then, you could try sterilizing a needle and using that to lance it, then clean it out with disinfectant designed for animals and let it drain. She’ll just wipe ointments off on her body feathers and dirty it again. Is the hen eating and drinking normally? What do you mean "some distress " ? Can you be more specific?