Udder/Ovary Question

My mare had an ultrasound a couple ago which showed one of her ovaries was larger than it should be. So vet scheduled us to come back in a month and do another ultrasound to see if it has gone down any, and then we will go from there. I noticed a couple days ago when I was grooming her, that her udder is also larger on the same side(the other side is normal size) that the ovary is larger. Any explanation on if/how this is related? We go back to the vet soon so I will bring it up with him, but I figured I would also ask on here ahead of time since I really don’t know much about ovary/reproductive issues in horses and if this is normal.

Thanks in advance!!!