Lymph & Liver Question

Hi, I work part time with a vet and I have a quick query for the forum

We had a girl in with an older west highland terrier last week that had fleas and a bacterial ear infection in both ears. We gave her aurizon to treat the ears and Advocate spot on drops to treat the fleas. Links to both treatments below (the spot on in the link may not be the same applied).
http://www.petdrugsonline.co.uk/site.aspx?i=pr183313
http://www.bayeranimal.com.au/default.aspx?Page=50&ItemId=38

The dog was in with us about 4 months previous with liver problems, with possible signs of a tumor growth on the liver. Which we treated with doxion liver support tablets (link below).
http://www.vetmedsdirect.co.uk/doxion-tablets-100mg-x-30/

The owner also decided to change the dogs diet to reduce the intake of toxins from commercial dog food in the hopes of giving the liver a chance to recoop. The dog reportedly improved greatly in health and had been doing well until the fleas and ear infection last week which like I said we treated.

Now today, the girl came back and the dog had swollen lymph nodes. She wondered if the flea and ear treatments could have caused the lymph nodes to swell, seeing as the liver is unhealthy and may not have been able to remove potential toxins in the treatments from the blood. After a bit of reasearch I have found that the chemicals in the 'spot on' treatment can be harmful.

The vet I work with believes it is lymphoma which is the obvious diagnosis but I'm not sure. She wants to treat with rheumocam (pain killer and anti inflamitory), noroclav (anti-biotic) and steroids which would do more harm than good if she's wrong.

So my question is this:

As lymph nodes filter chemicals and toxins from the body could they be swollen as a result of the liver being unable to deal with potential toxins comming from the treatments?

Any thoughts on the matter would be greatly appeciated.