[Ultimatejoe]

The hill of Cerin Amroth was hallowed long before Arwen kicked the bucket. Her death may have been inglorious, but I've always been of the impression that she quite literally lay down to sleep, and did. As for whether she became human, the answer is no. She decided to have her spirit judged with men, but her flesh could not be changed by any act short of a direct intervention of Iluvatar. After she died she was judged as mortal and her spirit left the confines of Arda to seek after her hubby.

As for her grave, I've always imagined that she lay there for a time, untouched, and eventually a hill formed over her in the same way a mound formed over the fallen bodies of the Battle of Unnumbered Tears in the Silmarillion.