Why do I hate my dads girlfriend so much?

I mean I respect her but after my dad died, she is trying to hard to help me which I appreciate but she needs to stop trying to be my mother. Told her the first time I met her that she’s not my mother and she never will be. Of course my late dad scolded at me for being rude to her and I better learn to get along because she isn’t going anywhere.
She once told me that even though she dating date (before he died) she is here for life and either I like it or not, she treats me like one of her daughters and she will be there for me and we have to learn to get alone and work together and it’s understandable that change is hard but it’s something we have to accept in life.
I thought she would stop talking to me after dad died but she checks up on me to see how I’m doing and I need to learn how to move on without my daddy and she told me that he would not be around forever. She said, “I told you your dad wasn’t going to be around forever but you didn’t wanna hear the truth so it’s the hard reality you need to face. Nobody is telling you the harsh realities because they’re too afraid to hurt your feelings, so I would have to tell you because I love and care about you so much. You’re naive about life so I have to be brutally blunt with you. You don’t get hints. I told you.”
That was harsh………