I wondered about anxiety, too.
My son had tendencies to rude to us (parents) and saying "you will not speak to me like that" only helped in the moment, it didn't seem to change behavior long-term. (Often, I think he'd just sulk/seethe that we'd cut him off.) And often, it seemed to come out of the blue. We finally ended up seeing a therapist who brought up anxiety. At first, I didn't see it -- he was a confident, successful kid. However, after a while I could. If he was stressed about Issue A, he would lash out about/hyperfocus on Issue B so he wouldn't have to deal with Issue A. Issue B was almost always directed at us, and was some sort of perceived shortcoming by us/perceived injustice to himself that we should have fixed/prevented.
My son has developed some coping strategies to help him manage Issue A before Issue B becomes involved. He has gotten MUCH better about it. It also helped us see what was going on so we could respond more objectively to him when he starts hyperfocusing on Issue B. It's easier to keep emotion out of it when you realize it's not personal. And, when he starts in on something now, we can say "I can tell you're really upset, but what's the REAL issue here. Let's talk about it." Sometimes he doesn't realize how much Issue A is affecting him, until he "takes it out" on Issue B. He's getting better at recognizing it, but sometimes there are still slip ups. It's somewhat easier now to get him to stop "spiraling" and figure out what's really bothering him so he can address that.
As an example: One of the most recent "outbursts" involved a 2nd semester elective class. When he signed up for it (last year), I told him I was surprised he was interested in that class becasue the subject wasn't something that I'd heard about him being interested in. But he said he wanted to take it, so... OK. In January, a week or so into the semester, he announced that he hated the class. The only reason he took it was because I "made him." I reminded him that I had *not* made him, and he replied that he only signed up for it because he knew I'd make him take SOMETHING-- and he knew I wouldn't let him do an extra study hall or early release, even though he didn't need the elective credit for graduation requirements. He may have been right -- I may have recommended taking something -- but we never even discussed it. I approved the schedule he said he wanted. And, by the time of this outburst, it was too late to withdraw from the class, so it was a moot point anyway.
I was able to talk through it with him and find the real issue. Turns out, it was about his AP Physics class. He was doing reasonably well, but he had recently found out that his teacher's students last year did not have a high pass-rate on the AP Exam, even the ones who'd done well in the class. (To earn college credit for the class, you have to pass the end-of-year national AP exam.) In his mind, he was worried about passing [Issue A] > decided if he had more time to focus on it, maybe he'd do better > he thought "Maybe I shouldn't have taken the elective"... and he refocused to Issue B! We were able to discuss possible solutions and that even the "worst case scenario" (not earning college credit for the class) was NOT the end of the world. Things have been better since then. The AP exam is next week, and he's still not sure how he'll do, but we'll get through it. I *wish* he could have recognized this in himself before it came to being rude to anybody -- it's still a work in progress, but it is a LOT less frequent than it used to be.
I am very glad that we got him into counseling when we did and didn't just chalk it up to "angsty teenager" (and I'll be honest, I wasn't really sure... but life was getting pretty miserable for all of us.) I am sure it will be harder with the OP's daughter since she's an adult and may not see it in herself. I do think sometimes successful, driven people are anxious because they feel like they have to keep being successful... every time, with everything. That can be very stressful... but there are definitely healthier way to handle it than being rude to the people who love you.