In truth she would be hard pressed to even get past the Thandol Span, and thats if the third party factions like the Ebone Blade and Argent Crusade didn't initiate hostilities with her (which they definitely would). I would say Tirion armed with the Ashingbringer. The weapon responsible for the defeat of Arthas would completely rule out a Forsaken victory. The paladins would carve a swath of destruction through the Forsaken ranks that they would not be able to recover from. plague or no plague. Val'kier or no Val'kier.