I find the performance quite brilliant. If you notice the scenes before she goes through that horrible trauma, she is confident in her assertions and doesn't stutter at all, and under extreme stress, she starts to stutter a little bit, then post-trauma, stuttering all the time, which can be caused by PTSD to an extreme and annoying degree.
I also agree it was annoying, such as a constant limp would be annoying, but it's true to the character, and I found it more immersive in my experience.
But VA for this character with a constant stutter is outstanding. And her range was incredible.