That sounds horrible, I feel your pain. I am in the exact same situation however my chatty coworker is not doing the same job, although they always want to be involved/meddle in whatever I'm doing nevertheless.
It's down to the level of reading out loud everything that happens on their computer screen. "Oh, I thought if you clicked there, something else would happen". "Oh, what's that?". blah blah blah. Total verbal diarrhea.
To top it off, they have a very, very loud voice.
If I make any comments to try and stop the incessant nattering, it's met with a snarky comment and only very minimal and temporary change.
My productivity has gone way down, it's almost impossible to get useful work done lots of the time, so I hardly try.
