Hello, I am Dr. Peter a licensed Veterinarian. I would like to help. I need to ask you a few questions to be well informed and give you the best advise. There is no additional charge for information request.
1- If her anus was a clock on what number would be the hole?
2- How long has this been going on?
3- Has she been rubbing her butt on the floor?
2. just noticed today
Also she did have a sore there in the winter a few years ago but it was not this bad. I thought it was her gland. It was always worse when she was in the cold. However it is not cold outside at this time of year.
The description of the symptoms you provide is consistent with a ruptured anal gland. When the anal glands become impacted they will herniate or erupt through the side of the anus. Other possible causes could be a localized infection, laceration, tumor, etc. But, most likely it is a ruptured anal gland. This is what you can do until she is seen by your family veterinarian.
1- Do not let her lick the sore or she will make it worst. Ideally, place an ecollar (cone) or you can place a t-shirt on her by sliding the back legs through the sleeves.
2- You can flush the sore with water for 5 minutes. Then, apply a topical antibiotic like neosporin or bacitracin. Do this twice a day.
3- Follow up with your family veterinarian they will need to express the anal gland and she may need additional medication.
Hope the above helps, if you have additional questions I will be glad to answer them.