How should I cope with my mother forgetting what she says?

It is becoming very apparent to me that my mom has moderate if not severe dementia. It is so hard for me to deal with the dementia that I feel like I am verbally abusing her when we fight. How do people cope with the person never remembering that they say things that are hurtful or constant complaining? It's really difficult also because she presents herself like a lucid person most of the time but then cannot remember that she's complained about a certain thing 10 times that day. Do I just need training or should she be in a nursing home?