I don't think that their relationship with Legolas ever comes up in LotR, so we really have a blank slate to work with. We can give them any relationship we want.Now we have to assume the Children of Elrond would visit Mirkwood fairly often for an elf or have extended stays, which changes the dynamic of their relationship to Legolas.
We have no active plans for Celeborn's sister to hate or get revenge on anyone. I don't think that has been suggested in this thread, ever. She will be involved with reconciliation between Noldor and Sindar in the main story. She will encourage Elf-Dwarf reconciliation in the frame. She won't take part in any warfare in the frame, or the main story. We have no plans to show her killing anyone, Dwarves or otherwise. There is no contradiction.
My desire to keep Galathil and Galadhon in the main Season 4 story is to kill Celeborn's relatives in Doriath so that he has a stronger reason for his eternal antipathy towards all Dwarves everywhere, and to ensure that we have named people still left alive to die in the battle that destroys Doriath.