Is forgiveness considered valid if it comes after a period of initial abuse and anger, knowing that the anger was internal? And is the ability to exact retribution a prerequisite for forgiveness, or is forgiveness valid even without the ability to do so?

Forgiving the wrongdoer carries immense reward, whether the wronged person is capable of retaliation or not. However, forgiveness when one is able to retaliate is greater in reward. Complete forgiveness is that which stems from power and knowledge, not from incapacity. Forgiveness when one is not able to prevail is considered forgiveness, but it is less than forgiveness when one is able to reclaim one's right from the oppressor. It is not a condition for forgiveness that it occurs immediately after the wrongdoing.