Elves made really light, elegant ships, and Arwen had gained a lot of weight
after the bearing of six children and six-score years of mortality and
Gondorian porridge.
So there was literally no ship strong enough to take her. Legolas, on the
other hand, ate 5+ a day and lifted
weights.
BOROMIR: One day our paths will lead us there, and the Tower guard will take up the call--the Lords of Gondor have returned!
ARAGORN: Dream on, mate. You'll be in the back row cleaning my shoes--did I just say that out loud?