I am sorry your dog is having trouble. It is very difficult to treat this kind of infection at home, as it typically requires antibiotics. Without medical attention, your dog can become extremely ill, not to mention experience a great deal of pain. Please see the following website for more information on mastitis.
I am afraid that there is not a way to treat this problem effectively at home, and that the longer you wait to have your dog seen, the more difficult and expensive it will be to make her well again. You can contact your local humane society or SPCA and inquire about low cost animal hospitals in your area. These hospitals offer services at lower prices, and may be more affordable for you. Please let me know if I can be of further assistance. If this has been helpful, please hit the green accept button. Best of luck with your dog :)