No more hair for her!
It's ok if she didn't like it. It happens all the time that people get haircuts they don't like! It's even ok that she told you that she dosen't like it. But to run her mouth about it in front of others is a case of her being an insenstitive drama queen. It's really unfair of her to put you in that position and to put you down in front of others. People who get like this will always be like this. You don't need it.
Tell her that you are sorry that she didn't like her hair, but that your feelings were hurt by her and you will not be doing her hair anymore. If she is out there complaining about her hair in front of you and hurting your feelings, there is no need for you to worry about hurting her feelings.