For the topic, I think it's just something like Arwen choosing to have a mortal life and then Eru who heard what her choice is will make her a mortal since that's her wish and she has that advantage of a choice. So, when Aragorn died, some years later, Arwen died too.
In general, for those half-elven who were given the benefit to choose between immortality and mortality, they (Arwen, Elladan, Elrohir, Elrond, Elros) just have to choose what they want then Eru will grant it for them and the rest is history. They will start to age, though their lives will still be longer than a common mortal, but it doesn't necessarily mean that it will change their physical appearance, they will not lose their pointy ears, etc.
Just to clarify, what I said were not officially stated by Tolkien (if they were, then YAY!!), but they're just my 2 cents.