We're not gonna talk about how big that scar is? That's a heavy blow right across the spine at least 2 inches across. It was also left open that way long enough to form the scar tissue. Maybe a healer got to her, but in most fantasy settings its timing. In other words, a healer wasn't able to get to her right away...
A deep gash across the spinal cord, splayed open for a period of time. I can't imagine the pain.