How much Accuracy do I need to hit Athena Pierce's Clone at a high rate?

At lv 70 (which I assume you will be when you fight her ), you need 127 acc for 100%, which you shouldn't hope for I guess. So you could settle for 110-120 which will give you 73-88%.

warrior accuracy works completely differently from archer accuracy. to archers, 127 accuracy is a joke. i dont know about hitrate, but i am under the impression that what is more relevent is how much damage you can do and not how often you hit.

you have 20 mins. and she can summon tauromacis.