We don't actually see them talk after her threatening, right? However, I do assume they got over that. My mind also says that although she forgave him, she did not forget. You don't get to see them close, or alone together at all afterwards. I'm not sure if she could totally forgive him. Like, when two people have a spat, it feels weird for a while, even after the fight is over. I do think though that she later on starts trusting him again, because there were no more threats even though he and Buffy are back being close (friends?) again.
I was also thinking about the scene from "Him", where Buffy and Dawn sit outside at the school's football field, and they talk about Spike. Dawn says that she doesn't understand how could Spike love her (Buffy) to death but then to it (rape) to her. She did not forget about that, but she's trying to understand, understand Buffy motly. To her it's clear that Buffy forgave Spike. So maybe she did as well. Because she was trying to protect Buffy, and Buffy assures her that she's fine with Spike now ("for the credit, Spike knew how wrong it was. That's why her ran away"), so Dawn could forgive him as well.
But the fact that they didn't speak to each other again, I think, like I said, she forgave him, but did not forget. It's a shame. But I don't think they could be back to what they were before. Not the same. I mean, she could talk to him, look at him in the eye, but still... it's not gonna be so easy to restore their past relationship. That's what I think.
