I would just wash her vent area in warm soapy water. Look for any redness or bare spots around her vent. Maggots from flies can be deadly if they invade a poopy butt this time of year. Trim of any excess fluff around her vent. If she is having some loose droppings, that can be common in hot weather when drinking a lot. New droppings will cling to the poop already there that dries. Usually with vent gleet, you would smell a foul odor, see raw bare skin around the vent, and she might have constant running poop.
Stop the ACV. Clean your waterers daily with soap and water, and replace with clean water. What brand of feed do you use? Some already have probiotics. The Rooster Booster Vitamins with lactobacillus is okay for a few days, but it has electrolytes which can cause diarrhea if used mire than a couple of days. A spoonful of plain Greek yogurt or a commercial probiotic can be used a couple of days a week. Probios powder is one easily found in most feed stores for all animals. Most vets have Purina Proplan Fortiflora that they can sell in packets, or you can order that or others online. In my flock there may always be one hen who has a chronic dirty butt, and it may be nothing wrong.