I dont userstand.

[Voralphion]

Galadriel was a much more powerful elf then Elrond

No she wasn't. In a letter regarding whether or not Galadriel could really wield the one ring it was implied that Elrond was in fact more powerful. (Sorry I don't have the quote). Simply being half elven does not mean he is less powerful, in fact in biology hybrids are often stronger than the pure parents. Elrond had the best aspects of both elves and men, as well as being descended from Melian, a maiar. Lorien may have been able to hold out longer due to the fact that Galadriel used her ring more. Also Sauron would send his full force against Rivendell is he was certain the ring was there, something he didn't do against Lorien.