It is common in close relationships that both people may have to forgive the other at the same time. There is nothing wrong with this. A key is this: Please keep in mind that each of you may be at a different point in the forgiveness process. For example, you may be very ready to forgive her, but she is still too angry to consider forgiving you. In a situation like this, I recommend that you go as deeply as you can in forgiving her and, at the same time, apologize to your sister for “dumping” your anger onto her. Your apologizing may aid her process of forgiving.