It is not only the verbal hatred but that awful look of hatred in the eyes. But you do have to not let it fester within, the person with dementia has forgotten it all within minutes. Sadly it does affect feelings towards them, but for self preservation you have to try to find ways around it, learn to become "thick skinned". Not easy.
Sheila, all you can do is wait and see if your cousin eventually comes round, but not easy for her when she knows what you did not know about past family conflicts. Plus possibly your aunt's behaviour brought pain from remembering her own experiences with her late father who had AD and sounds to have been aggressive in speach and physically to her and her mother. Possibly a combination of both, if she is not the crying type. I am sorry.
Yes, it is a funny old world. I remember at my father-in-law's funeral his sister tore into their late sister's daughter about some past feud and the poor girl knew nothing about it, not having been born when it happened.
Hope you are feeling better, your cold and cough easing.