I'm no expert on these things, but I think the important thing is to convey the message that the problem is within yourself, and not her. You don't want to make it sound like there is something wrong with what she's doing, because she's just having some coffee. The problem is your own sensitivity, which you acknowledge is kind of unusual. (Unlike people who microwave popcorn in the office every day, with that nasty fake butter flavoring which stinks up the building. They really are trying to make the rest of us retch, and ought to be beaten upside the head.)
So, I think if it were me, I'd probably say something like,
"You know, this is really, really weird of me, but there are certain noises that just make me feel all tense for some reason. One of them is the sound that the coffee makes when it's getting poured into that flask. Do you think maybe you could pour it someplace else, or when I'm not around, or warn me first, since I've got this crazy sensitivity to the sound? It's kind of my version of fingernails on the chalkboard." [Most people, even NTs, seem to relate to the "fingernails on the chalkboard" feeling.]
Actually, that's the kind of thing I think is the best thing to say, but honestly I would be nervous about saying anything, because confrontation of any sort is very difficult for me. And of course, it depends on the coworker. I've had a lot of coworkers that you can't say anything to or they'll twist it around into a personal attack, and next thing you know, you're in the boss' office listening to a lecture about attitude.
It's a pain, isn't it?
I'm having the same issue with my husband and his daily bowl of cereal. I haven't been able to say anything, because no matter how I try to phrase things to say, "You are not the problem, and I am not criticizing you", he takes it that way. He eats this crunchy cereal, and the sound sets me on edge. He keeps opening his mouth to take a breath, and when he does so, it amplifies the crunching sound. Also, he puts way less milk on his cereal than I would, and I can't bear to think of eating the cereal that way. I can't sit with him when he's eating it, or I'm likely to get so annoyed I start saying things like, "Have you considered breathing through your nose?" Once in a while, I try to playfully say, "What crunchy cereal!" as if I'm making an observation but I'm not freaking out about it. Still, he gets all hurt and defensive.
Personally, I can't stand earplugs. I hate the way they feel and the way they make it so that I can hear my own blood circulating and my jaw creaking.
Good luck.