Many states offer a free or low cost necropsy.
https://www.aphis.usda.gov/animal_health/nahln/downloads/all_nahln_lab_list.pdf
Look in that PDF for the lab nearest you and see what they say.
Glad you were able to get a tube and are tube feeding. As for what will happen to the lump? I really don't know. , guess it depends on what the lump was caused from. You might want to start weighing her daily to make sure she's getting enough to eat. In another post you mentioned giving her 125...
Prednisone is one of those drugs that's almost impossible to get without a prescription, so I wouldn't bother... Tube feeding will keep her from dying of dehydration and starvation, so that's why I suggested it.
Wow, never seen anything like that. Do you have any prednisone? I wonder if that would help? If she were mine I would tube fluids, then baby bird food.