lumps on my 7 yr old female German Shepard

Question
She was poisioned June 24 2009. We had to take her to a new Vet. The vet did save her life but since then I changed her food and she got real sick this was about a month ago. I did take her stool to her old vet and htey told me it came back ok. I noticed she went in heat around 2weeks ago. She seemed to be panting more and seemed to be drinking more. Around Sept I had given her a bath and noticed a raw spot under front under arm. I thought maybe it was the shampoo so i put some cortisone on it everything was fine. I thought I was doing everything possible for her. I changed her back to her old food re bathed her. She has seemed to be eating and drinking good. Now yesterday I noticed she had a lump the size of 50 cent piece in her neck or on the side and today I found a small knot under her left under arm.She has been through so much since someone tried to kill her. I did have a 8 yr old black AKC male shephard to but the poision killed him. She had went blind and that day the vet kept her and gave her doxicline,predisone, a vit. The new vet did not tell us she could get cancer.I'm afraid that is what it is. She did have enlarged ovary the xray showed that when she was poisioned. how can I tell if it is cancer or can her lymphones swell from something else. She is very skinny but remember i had changed her food and didnot know that could cause har to have loose bowels and did not want to eat. The stool sample came back no bacteria and no parsites. She is very playful and has got back her to eating like she should.Now this has to happen. She has never had puppies. Waht can be done if I take her in to the Vet. I have already spent 1000$ to save her I thought. She did get all her eye sight back actually the next we went to get her from the vet she could see great..I have read a few things about the lymphones and I'm so scared...

Answer
If there is a wound, then the lymph nodes are responsible for draining the area and making immunity from the infection.  That does not mean cancer.  Before jumping to any conclusions, let the vet look at it and possibly take a fine needle aspirate of the mass to see what it might be.