If you are 100% positive that no entire dogs got anywhere near her, you have nothing to worry about.
My pup had her first season at 7 and half months old. Within three days of the season starting, she had big nipples. She has gone on to produce an udder that resembles a cow that is overdue for milking. She is now 60 days since the end of her season and is digging and nesting, no belly though and definitely no pups there. I know that because I watched her like a hawk when she was in season, her breeder has looked at her and told me her mum does exactly the same thing. In fact, her mum actually delivered waterbags around her due date.
If your boy has no testicles there is no way he could have impregnated her. He may have tried and succeeded in tying with her, but would be shooting blanks. My boy who is 6 was desexed as a pup but he still tried occasionally with the girls when they are on heat (only because they ask him too).
I don't think you need to see a vet, there is nothing you can do, just ride it out. I have tried extra exercise with my girl to no effect. She still has a huge udder, and, she has dropped a lot of what little coat she had and the feathers no longer hide the baggy boobies. Doesn't seem to worry her though. I was concerned she may get mastitis but she has had no redness or heat down there. Oh, and her vulva has not shrunk back to it's puppy size either. I'm hoping it will all be over soon.
