When you state what God must do that's presumption. And no, we must not do anything. We have free will to do as we please. Just as God has free will to do as he pleases.
As for your situation, I don't know what she did to you, but please don't take it out on me. Forgive her, don't forgive her.... I couldn't care less. All I know is that we will continue to have lessons brought back to us until we learn from them. So regardless of what you choose to do, you shouldn't necessarily expect things to work out as you expect.