Sofia is the assertive woman that Celie is not. She won’t back down from a fight and if anybody picks on her, she beats them twice as hard as they give it to her. Celie admires this quality, but often times it just causes Sofia trouble. Her assertive nature tends to rub white people the wrong way.
In addition to her assertiveness, Sofia is also extremely honesty and willing to act on her emotions. When she struggles, she says so. When somebody hurts her, she says so. When she’s mad, she acts on it. This is also, of course, what gets her in trouble. Celie never emulates Sofia, but Sofia serves as a visible reminder that Celie doesn’t have to take everything lying down, she can learn to stand up and fight.