So far, Arwen has Glorfindel's part and stolen Frodo's thunder at the fords. I expect she has Halbarad's part and probably her brothers' as well. If she take's Merry's part as Nazgul-slayer all the elf-bashing promises are off!!!
If Merry is cut from the Nazgul slaying scene, I highly doubt that it would be Arwen there fighting with Eowyn! Nonsense! - Tomfoolery!