People who are critical are excruciatingly insecure and feel the need to control;. I recommend the book that saved my life: THe Verbally Abusive Relationship by Patricia Evans.

Boundaries by Townsend and Cloud is an excellent resource.

"handle criticism better" That is typical; she doesnt want to own her behavior and wants you to tolerate her verbal abuse. yes, therapy is the answer....by yourself; I am guessing she wont go because she doesnt think she has a problem.