Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that your pup has been definitively diagnosed with an osteosarcoma in her left rear leg.
I am sure that was devastating news to receive in a relatively young dog.
Unfortunately in almost all cases by the time we find the primary tumor it has metastasized at at least a microscopic/cellular level to filter organs such as the lymph nodes, lungs, liver and in some cases the spleen. It also like to spread to the brain.
Traditionally the recommended treatment consisted of amputation of the affected limb and follow-up chemotherapy. While this isn't curative it does prevent pain (which will become a problem as the tumor grows) and slows metastases and their growth rate.
I don't know where you live in the US, but there is some very promising research being done at the University of Pennsylvania School of Veterinary Medicine with immunotherapy and radiation. They are finding vaccination with a tumor-targeting cancer vaccine, combined with radiation therapy, can decrease bone cancer pain and prolong overall survival in dogs with osteosarcoma.
Here is a link to their web-page: http://www.vet.upenn.edu/about/news-and-events/press-releases/article/penn-vet-recruiting-dogs-for-bone-cancer-vaccine-clinical-trial
I don't know if they are still recruiting patients, but I would at least contact them to see if they are, or if they know of other Universities that are doing any similar trials.
I found a few others that seem to be working on trials for treating osteosacomas:
1) Florida: http://research.vetmed.ufl.edu/clinical-trials/small-animal/vaccine-study-for-dogs-with-osteosarcoma/
2) Colorado State has a few different trials: http://www.csuanimalcancercenter.org/clinical-trials
3) Texas AMU appears to be researching a novel chemotherapeutic agent eRapa : http://vetmed.tamu.edu/clinical-trials/canine-oncology
4) University of Wisconsin has 3 different trials going: http://uwveterinarycare.wisc.edu/clinical-studies/oncology/
I would not bother with any of the "naturopathic" or "homeopathic" medications. This is an aggressive cancer that needs directed therapy, and even then we often don't win. I have heard very promising results about immunotherapy, but all of these universities have excellent reputations and if you are interested they would likely give your pup a better chance than the current treatments.
Best of luck with your pup, please let me know if you have any further questions.