Arwen is found having been released into peace. We see the Elf from above, a perspective which allows a number of points to be made in the composition.
Arwen wears her hair in such a way as to cover her ears. Arwen has chosen the mortal life and signifies this by covering the outer signs of her race.
Arwen's arm is held out in utter submission. The release from immortality has been a voluntary act.
At the same time the hair is spread outwards suggesting floating. Arwen appears to have floated out of living and has been carried upstream to the afterlife.
The pattern on the tiles is that of interlocking circles enclosing a star. The star is a symbol of the elves as is the spiral or interlocking circles. The tiles are covered with dead leaves, reminding us that death is not final. The dead leaf is not the tree.
The red cloak spreads out from behind the figure giving it an angelic quality. The choice of red recalls the phoenix, a symbol found in Rivendell. There is a hint of renewal, change and an upward progression.
We are reminded of the twin symbols of the phoenix, with it's outstretched wings, together with stars and spirals. This decoration is everywhere in Rivendell. The composition of Arwen then suggests she has found peace and harmony with her kingdom.
Arwen here is surrounded by as rich a connection with her world and nature as Ophelia is in Millais famous depiction.