My 10 year old daughter has had a sass issue for many, many years, and it is partly because she gets over-excitable. In her case it is a gifted issue too, and she has been tearful when I confronted her (at age 7) with how I felt about her sass. She really had a hard time stopping herself from getting irritable and really did not mean to hurt my feelings. I had to relieve her from the guilt resulting, because she was just irritable, and not able to handle all the feelings.
So now I state calmly that I don't like the behavior and I ask her to apologize and then I accept the apology, but I don't talk anymore about hurt feelings. We are calmly discussing the whole topic of respect. I am seeing huge improvements because she realizes I am not judging her, and she sees the issue now as about her self control, when she is irritable of over-excited. We also have ways to work out our problems, without yelling, and that is important too.
I think it is important to discuss the topic when the behavior is not happening. Also, she may have legitimate gripes - triggers for her sass, and you can calmly discuss these, so that she realizes that gripes can be dealt with constructively and sassing and yelling is not okay for either child or parent. If you are a yeller, or make put downs at her, you will have to stop these behaviors too, to be consistant.
Adolescence is a chemical roller coaster for youth and reading about this together may help. It may be that she cannot stop herself from feeling irritable at times, because of what is going on in her body(adolescents have low dopamine "feel good chemical" levels in their bodies, that is why they get so moody at times.)
If your daughter sasses when she's irritable.... if that's what you discover, perhaps the response from you can be to calmly remind her of family rules about communication, but not mention hurt feelings . Perhaps you can also support for her taking care of her mood in a repsonsible way. We have a tea ritual in our house, as a way of taking care of each other. At this point, offering tea or cocoa is a signal of support, that short circuits the yucky communication cycle. It's saying also "let's drop this fight -- lets realize we are not at our best and break this cycle, right now.. regroup, calm down.
D.