My MC’s arm got brunt to the bone in her hand/wrist, to the muscle (and a bit further) to the elbow and to the muscle from her elbow to her shoulder. She lost her nerves from her elbow to her fingers and the feeling comes back from her elbow up. She gets some treatment, mainly just ointments/herbs. She has 2 years until she joins the military. Would that be enough healing time? How would this affect her fighting? She fights in a style similar to tai chi, ninjato and teakowndo, does this matter?
Oh god, I can already tell this would be a nightmare to fully research. What you’re describing is a fourth degree burn… well, technically at least three fourth degree burns, requiring surgery, and possibly, in this case, amputation.
If your character has had enough of their arm burned away to destroy the nerves running down the arm, then everything “south” of the burn will be paralyzed, including her hand. If the burn also destroyed the artery in the arm, which is possible, then the tissue beyond the burn will die and proceed to rot. Technically this is called “tissue necrosis,” or gangrene, but, the reality is far less clinical and more horrifying.
Even if that’s not the case, third and fourth degree burns both carry a pretty serious risk of infection. For someone in a pre-modern setting, without an understanding of bacterial infection, and without access to a sterile operating environment? This is probably a death sentence.
Long term survival for burns like this, usually involve grafting tissue from elsewhere on the body. In that case, arterial grafting is possible today, though I don’t know how old that particular technique is. Muscle and skin grafts have been around for awhile. From what I can tell, nerve grafts are still semi-experimental, the technology is getting there, but it’s still tricky.
But, for a character limited to herbs and ointments? Unless they’re explicitly magical, and you’re in a setting where magic can repair egregious injuries like this? No, that’s how your character died, not a thing that happened to her before she started serving in her military.