That looks like a totally normal vent.
What are the conditions of the coop? A large pile of poop in hot, humid weather is definitely an open invite for maggots. This is the time of year for flystrike. Flystrike often occurs when there is a buildup of poop around the vent area, and flies lay their eggs in the poop which can eat through the chicken's skin. It can be deadly. However, I do not see an evidence of this occurring on your girl. I would suggest cleaning up the poop in the coop though if there is so much that maggots are present.
Here is an excellent, and short, video featuring a healthy chicken vent, and the presence of mites.
Neither poultry dust, DE, or deworming is what is needed to be rid of maggots. Just cleaning the coop.