My Ten Year Old Lab Mix Started Limping And Holding

My ten year old lab mix started limping and holding her right paw up about a month ago. I took her to the vet and they did a blood test and said she was slightly anemic, so to feed her senior food instead of the science diet for sensitive stomachs. There has been no improvement in her walking, in fact she seems in more pain and refuses to go on walks. Today I noticed a large area under her right front leg that looks like a large hard lump of about 2 inches by 3 inches that is very flat to her skin. I wonder what i should do? I do not know if anything could be done to alleviate this so she could get back to walking, that she loves to do.