I absolutely think Arwen should have joined Helm's Deep, and then continued forward with Aragorn for the rest of the story. After all, Elrond's sons hook up with Aragon and go on the Paths of the Dead with him. God forbid we have a female character actually participate in the story. ;-)
We do, just not in the same role as Aragorn. The Paths of the Dead were butchered in the movie anyway. So much of the story comes from Tolkien's experiences in the trenches - leaving family behind to fight in a foreign land, beside men who start out as strangers or even enemies but through the crucible of battle become lifelong friends. Having Arwen at Aragorn's side changes the entire dynamic of the story.
A purist who wants Arwen At Helms Deep? Sounds like a steak-eating vegan to me...***And I say this as a huge Tolkein purist who's read the novels like twenty times.
Part of the adaptation process, sometimes.
Also, with due respect to everyone, the Path's of the Dead in the book had Aragorn joined up with Elladan, Elrohir (Elrond's sons) as well as a company of Aragorn's Ranger/Dunedain kin to join him on the Paths of the Dead.
So, I do understand your point about Tolkien's experiences in the trenches translating in to LOTR, but I think that better applies to the Fellowship more than, than that chapter.
However, I will agree that the Paths of the Dead could have been done better in the films.