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- To make certain we are speaking of the same area, when you say bottom you mean the butt or bottom of the belly?
i mean it is directly adjacent to her butt and its very red/pink and swollen.
1- Has she been rubbing her butt on the floor?
2- If her anus was a clock at what number would you put the swelling?
The swelling that you are seeing is consistent with an impacted/infected anal gland. When the anal gland becomes occluded and the secretion has no where to go, the gland can become infected and rupture or herniate through the side of the butt. What you are seeing is the swelling the preceeds the rupture.
Treatment involves expressing the anal gland and placing her on oral antibiotics and anti inflammatory medications. For now, do not let her lick the area or she is going to make it worst.
To avoid this problem in the future, she should have her anal glands expressed every couple of months; no need to see the vet to have them expressed; groomers often express them. A good indicator that the glands need to be expressed is when the dog rubs their butt on the floor. Follow up with your family veterinarian.
Hope the above helps, if you have additional questions I will be glad to answer them.
There is a good possibility it will rupture. If you can have her seen now it would be better. But, this is not an emergency that is life threatening it can wait until the morning.
To stop her from licking place a t-shirt on her to cover her butt. Slide her back legs through the sleeves and tie shirt along the back.