TYPE-MOON Fes. 10th Anniversary Q & A: Q: It has been said that a certain Aozaki cannot even defeat a serious Caster, is this "certain Aozaki" Aoko Aozaki? Is this an assessment based on Aoko using True Magic?
A: "A certain Aozaki" includes both Aoko and Touko. In a magecraft battle by modern standards, a "magus" who is capable of defeating a serious Caster does not exist
Source: http://typemoon.wikia.com/wiki/Aoko_Aozaki
References section.
I don't know of Aoko's powers or feats but if word of god says she can't even defeat a serious caster, how can she win when it's Lancer, Saber, Archer and Berserker? No argument with Arcueid. Arch-type earth was stated to be the strongest character in Type Moon even surpassing Void Shiki so she can definitely kill any servant. She might have a hard time against Serious Gilgamesh though.