it seems like she wants to gain power over all vampires and she is using the blood tablets mixed with her own blood to do it, the only problem is that kaname intends to kill all purebloods including her and she knows that she cant stand up to him, and in the past chapter 73 "relations with zero" it showed what yuuki, maria and maria want from him and where they stand, it shows that yuuki wants to be by his side, maria wants him because he is a lot like ichiru and has his blood, while sara might want zero to kill kaname for her because he is the only one powerful enough to go against him
well thats what i think anyway, i just wonder if yuuki will go against kaname or let him do as he pleases