First, well done for accepting that you might need help with your self confidence, and more importantly, for going out and getting that help in the form of counselling.
This will hopefully build your sense of self worth, but you must not let your mother undo all the positive gains that you will make through your counselling.
As Sharon and Wolf have said, you need to get as much time away from your mother as you possibly can. She is a toxic influence on your self image, and she is unlikely to change. Somehow, I think, she feels more powerful, more in control, when she is able to make you feel small and worthless.
Don't let her do this.
If you can, move out of the house and try to find more independence and autonomy.
That, together with your counselling, will build your self esteem and you will find that you are better able to stand up to your mother's criticism.