My dog has been nursing and she now has mastitis, please help!?

We don't have leash laws around where we live, so some people a couple streets over let's their many dogs roam where they please. I fell in love with one of their dogs, who was very underweight and covered in fleas and ticks. I asked the owners of her ( her name is Duchess now ) if I could have her, and told them the home she would have etc. and they agreed. I took her to the vet and they said she was probably going to have puppies, so I should wait on getting her vaccinations, but I did get her started on heart-worm preventative. The day after I took her to the vet she had two puppies. The vet wasn't sure because to look at her you NEVER would have said she was about to pop out puppies! She is putting on weight now, slowly but surely. The puppies were three weeks old as of Saturday and are teething. Duchess now has mastitis due to the puppies teething and I plan to take her to the vet ASAP but its a holiday weekend, and I don't have any emergency vets anywhere close. I have been researching how to care for her, but all I can find is to use a warm wash cloth and try to work as much of the infection out as possible. If you have any idea how to care for her in any way I would HIGHLY appreciate it. I love her to death and don't want it to turn any worse. Thanks in advance!

Heat is about all you can do. Most breeders use a hot water bottle - being careful its not too hot and burns her. Make sure she's drinking plenty of water and make sure that whelping box is kept really clean. She needs the vet as soon as you can get her in because the vet needs to make the determination whether or not she needs antibiotics.