It sounds like you've done a great job trying to correct Angels problem.
The Malacetic wipes are a good option for cleaning her vulva however, some dogs can be sensitive to Malacetic so watch for any increase in skin irritation and stop using them if this occurs. There is another wipe called Duoxo that may be helpful if she has irritation from the Malacetic.
Weight loss is also an excellent idea. It can take some time so stick with it.
It's possible that Angel may have an underlying allergy that is contributing to her vulvar irritation and feet liking/chewing. If she has food allergies you may be able to significantly improve her vulvar irritation by putting her on a hypoallergenic diet trial. This means feeding her a diet with a new protein source (duck, venison) and a new grain source (potato). There are several veterinary diets and some diets you can get from the pet store that contain these ingredients. You will need to feed her this, and only this, food...no treats, rawhides, people food etc for 8-12 weeks. It is worth trying especially if you are planning on adjusting her diet to try and get her to lose weight.
With negative cultures and microscope slides antibiotics will probably not be helpful. Some dogs do respond to steroids or antihistamines for allergies. You would need to get the steroids from you veterinarian and discuss the potential side effect with them. You could try antihistamines (Benadryl) at home at 1mg/pound every 12 hours. So, if she weighs 20 pounds she would get 20 mg.
You also want to prevent her from licking her vulva as this will increase the inflammation. Use a collar is necessary. If she is scooting her bottom on the ground get her anal glands expressed. the scooting may stem from anal gland irritation and this can make her vulvar irritation worse.
Good luck with Angel