Katniss's mother was not originally from the Seam. Her parents had been merchants, selling medicines to officials and peacekeepers in the nicer part of District 12. She moved to the Seam when she married Katniss' father. Since she was not native to the Seam, she did not have the tell-tale dark hair and grey eyes typical of the region. On the contrary, she had blue eyes and light hair, which she also passed on to her younger daughter, Prim.
Over and above her physical appearance and origins, Katniss' mother stands out due to her abilities as a healer. While she has no medical training, injured people from all across District 12, and later the country, are brought to her when they are sick or have been wounded by Capitol soldiers.