Wow.....you just described the lady next door to me. Yes, this woman in your class is VERY toxic, majorly insecure, manipulative and probably a pathological liar as well. You're right to stay away from her and ignore her. And the others advice on not telling the workshop leader is good. I agree with them on that. It won't help your situation much and may very well just make it worse. And I also agree with the others that the people in your group will not base their opinion of you on what this woman says. In fact, most women and men for that matter know that a person that speaks unkindly about someone behind their back to others, will do it to them as well and are not to be trusted or believed. They are called "backstabbers" and "gossips". And they rightfully have a bad reputation. Just hold your head high, make friends with others in the class and ignore this mean, small-minded woman. Karma will come back to get her. It always does. Seen it many times.