I worked with 8-12 year-old sexual abuse survivors in a therapeutic group home for a year just after I graduated from college.
The aftermath of childhood abuse can be intense, and one of the notable things about it is how hard it is for adult caregivers to deal with.
If what this means for your family is that you have to use 1,2,3 Magic 10 times a day, you've gotten off lightly. I understand that your dd is frustrating, and that you aren't in love with this disciplinary method. But if it works for your dd, you should work with your therapist on embracing and celebrating that.
For comparison, some of the kids I worked with had homicidal ideation. Some of them needed to be restrained multiple times daily. A couple of them had command hallucinations. In the year I was there, every single client I worked with had at least one psychotic episode. These are things that do not respond to a count of three. With the kids I worked with, we didn't even consider a behavior problematic if the child could self-correct with a verbal prompt (like counting to three).
It's pretty typical for 8 yos to have episodes of rudeness. It's part of the process of testing their power in the world, and testing the people around them. A history of abuse can make this normal developmental pattern much more intense. It sounds like both you and your dd are receiving therapy. You should talk with your therapist about setting appropriate boundaries on rude behavior and devising a calm, consistent, predictable response (or adjusting your feelings about 1,2,3 Magic, if you are already using that calmly, consistently, and predictably). You might still feel frustrated at the end of the day. Honestly, that's OK, as long as your dd is safe. Tomorrow is another day, and the days will gradually get better.
ETA: I missed your sig! With a 4 week old baby and twin toddlers in the house, I bet sibling rivalry is playing a HUGE part in this right now. Let yourself love whatever works, and give your 8yo as much time and positive attention as you can. And get as much help as you can in this difficult time.