At my dojo, there's this girl I know who is a 1st kyu and a pain to train with.
Every time we train together she opens a full verbal assault on me on how I need to spread my stance wider, how I need to twist my stance this way and that way, how this would work and that would not work. Practically I never get to do a technique with her because she would stop me at any "error" she detects, and make me restart from the beginning.
I appreciate her trying to help me learn, but frankly she is not the best person in the class in a position to give instructions, especially when they are not solicited. And how do I improve without doing the techniques (and failing), all the same time getting my ears tortured?
Generally I have just been avoiding training with her but recently it has gotten really awkward since she can tell that. We hang out as a group off the tatami too, and this creates unnecessary tension.
How do I deal with this kind of situation?
Talking to your sensei or another sempai about what is expected can be a good place to start. Asking her opinion on your dilemma regarding missing out on technique would be another great way to directly diffuse that tension, although you'll have to accept that she probably will have an answer that suits her and might not suit you. One thought though, techniques can be useful, but so can your stance. I'm not sure how long you've been training but the first thing I tend to "correct" (try to the best of my ability) is that basic starting posture/stance.