How is Katniss's mother different from other residents of the Seam?

To reiterate what another educator already said, Katniss's mother has a skill for healing and for making medicines from herbs and resources found in District 12. This becomes extremely important in Mockingjay (and even in Catching Fire) when she has to help to mend the wounds of some of our main characters.
Katniss's mother gradually becomes a stronger figure throughout the novels. In the first novel, The Hunger Games, Katniss's mother is different from others in the Seam because she is relatively helpless compared to them. Other people in District 12 are more self-sufficient and crafty, while Katniss's mom is seemingly still grieving the loss of her husband. She seems to be in a fog much of the time, so Katniss, with her hunting skills and no-nonsense attitude, becomes the family's primary caretaker. However, when Katniss needs help, her mom is able to step up and become a more assertive character as the series goes on.

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.