First, let me warn you that this question is strictly opinion-based and subjective. While one person might say that there is indeed forgiveness and support that opinion textually, another person can just as easily take the opposing side. I will offer my opinion, but if you compose an answer for a class assignment, it should be in your own voice.
I do not believe there is forgiveness in Sula, but I do believe the two protagonists experience a catharsis from the negative feelings they have held toward one another. Nel goes to visit Sula on her deathbed when Sula is in excruciating pain. She feels morally superior to Sula by making this gesture, but she is quickly stricken down by Sula, who feels no regret about the way she has chosen to live her life, including sleeping with Nel's husband. She says that to her, the event was just another sexual encounter, but Jude was the one who chose to leave the marriage. Nel leaves unfulfilled, and Sula dies soon after. Sula's last thought, thought, is of Nel--the one person she ever truly loved--and of how she wishes she could share the moment with her and reassure her that death does not come with pain. Likewise, after the tragedy on National Suicide Day, Nel realizes that despite all the conflicts throughout their lives, Sula is the only real friend she ever had. It is only then that she allows herself to grieve for not only the loss of her best friend, but also the loss of her life to being what others expected her to be.
I believe one of the biggest forgiveness acts that occurred within the book is when Nel forgives Sula. When Nel catches Jude and Sula having sex, she is heartbroken and unsure how to react. This is the one cause that drives their friendship apart. However, when Sula is really sick and they finally talk to one another, Nel learns that Sula had no intention of hurting Nel, but simply viewed this as a sexual act. Similarly as they had shared talk about boys and everything when they were younger, Sula believed this was also okay. When Sula dies she still has no resentment in her heart and in fact wants to tell Nel that dying does not hurt, and as Nel is walking in the street she finally realized who she was missing the entire time, not Jude, but it was in fact Sula.