[elbenprincess]

Simply, because Sauron was much more powerful then Galadriel and to do so was impossible for even the Valar to do. Tolkien explains what could be done in detail.

Morgoth was more powerful than Fingolfin and still was wounded by him, he was more powerful than Luthien and still was put to sleep by her so why is it so unbelievable that Galadriel could read some of his thoughts? That doesn´t mean that she was more powerful than him in generel, just that she had an edge oder him in these matter perhaps.

Even among the elven ring holders, Elrond is the most likely to be able to defeat Sauron, not Galadriel in a personal confrontation.

That is NOT true!!! I guess you assume that because of that:

it appears that Galadriel conceived of herself as capable of wielding the Ring and supplanting the Dark Lord. If so, so also were the other guardians of the Three, especially Elrond. But this is another matter.

That is out of context, that is the full quote:

Of the others only Gandalf might be expected to master him – being an emissary of the Powers and a creature of the same order, an immortal spirit taking a visible physical form. In the 'Mirror of Galadriel', 1381, it appears that Galadriel conceived of herself as capable of wielding the Ring and supplanting the Dark Lord. If so, so also were the other guardians of the Three, especially Elrond. But this is another matter. It was part of the essential deceit of the Ring to fill minds with imaginations of supreme power.Confrontation of Sauron alone, unaided, self to self was not contemplated.

Both, Galadriel and Elrond thought of themself that they could master the ring, especially Elrond, that was due to the power of the ring. Only Gandalf could master it.