Are you sure shes not pregnant, is she in heat?
Treatment would depend on the problem. Is she acting normal; eating, drinking and active at her normal levels at least? Any fever or are any hotter than normal, hard, or red? Is she in heat or was she? That's pretty common. False pregnancy is an option. There may be something off with her hormone levels. Dogs actually get breast cancer and tumors and is particularly likely if she's not spayed or was spayed much later. They can also get an infection (usually one called mastitis). Have they always been that way or has she had pups? Since some of those are serious I'd call your vet and explain everything and see if they think they need to see her to be able to tell if it's normal or a serious problem that needs treatment.
False pregnancy it will go away on its own if it is all the nipples.. If not then it could be a infection and the vet will need to see her but it sounds like a false pregnancy
She isn't sharing the house with a young pet or child is she? It might be strong maternal instinct causing her to approach lactation.
She might just be inheat and looking for a mate but I really do not have a good answer