Very large lump in dogs leg? Help!?

Three weeks ago I took my 7 year old mastiff into the vet because her back left thigh swelled up about twice as big as normal literally overnight. She had begun limping 4 days prior, but i umed she slept on it wrong or twisted her ankle. But that morning when it was swollen she was crying and holding her leg completely off the ground. Our vet examined her and ended up taking xrays and a biopsy of her tissue. When he cut in to the tissue for the biopsy the swollen area popped and leaked out fluid. So our vet and the other vet decided to remove the metal plate she has in her leg due to a pevious injury. They were uming her bone was having an allergic reaction to the metal plate. I took her in for her two week check up and the swelling went down but know there is a huge lump in her thigh that is very hard. Her thigh is about 2x larger then it should be. It feels like bone. And she cannot bend her knee hardly. She is still in a lot of pain. The vet said to take her home and in two more weeks if there's no improvement he want to give her another xray and actually take the biopsy. It's almost time for her appointment and there is absolutley no improvement. I'm considering taking her to a orthopedic specialist instead. Can anyone help me figure out what this might be?