That does sound very frustrating!

When she says these things that hurt your feelings, do you tell her? You might say something like, "That comment makes me feel like you don't believe in my future. It really discourages me. Could you please be more positive?"

My mother can also say some really irritating stuff. I've finally accepted (more or less) that she isn't going to stop. It's just the way she is. My suggestion would be to stop trying to have a good discussion with her about your future. She can't give you what you are looking for.