My mum used to put me down too, to the extent that I developed a whole new persona in order to deal with it. I can honestly tell you, I don't even know who I am now, but I'm on a journey to find out.
Fast forward to me becoming an adult and an older one at that! I have often reflected on some of my actions, responses and decisions throughout life, and like you, have questioned myself. Maybe I am the "selfish" person she told me I was from the age of eight until forever. Maybe I am the no-good excuse for a human being she seemed to think I was back then. Maybe I am actually a crappy person and that is that.
Regardless of the quality of the person you are... Believe this:
SHE HAS / HAD NO RIGHT TO IMPOSE HER "OPINION" OF YOU, ON TO YOU. As a young person.
Sheesh... It doesn't matter who we are (because we will all face the consequences of our actions inevitably), the simple face is:
THESE PEOPLE HAD / HAVE no RIGHT to speak to us like that.
Ignore who she says you are. It is only coming from her expectations and perceptions of life, it is not ultimate reality.
As an adult who went through this thing for way too many years, I would cut my time with her, minimize it or go NC of you can, and use the time to reinforce who you really are, and cease letting her "define" you. What she really owes you is unconditional love (she made a decision to have children), but you may never get this.
Go off and find yourself, and only then will you ever know if what she's said is true or not, and if it's true.. bug deal. Nobody is "perfect" afterall.
Good luck to you :)