Does God hold us accountable for hating someone who previously harmed us, and for wishing for God's punishment upon them, without showing these feelings or harming them?

A Muslim must love, hate, be angry, and be pleased for the sake of Allah. This is among the strongest bonds of faith, and not merely for personal whims or self-triumph. Rather, one should pardon, forgive, and overlook if the matter pertains to oneself. Allah Almighty says: (And that you pardon is nearer to piety) and (So whoever pardons and makes reconciliation - his reward is due from Allah).

"Wealth is not diminished by charity, nor is a servant wronged and he endures it, but Allah increases him in honor." We advise pardoning and overlooking harm, and responding to ill-treatment with kindness, as Allah Almighty says: (Repel [evil] with that which is better, and thereupon the one whom between you and him is enmity will become as though he was a devoted friend). If you are unable to do that, then do not supplicate against him with more than he wronged you, and pardon is better.