Drinking too much water?

My wife, a professor and classical archeologist, had her first symptoms of ALS 2 years ago. The official diagnosis came a year ago June. Her first symptoms were in her legs, and the disease has progressed rapidly. She now has essentially no control over any limbs, cannot turn herself over, etc. Her first symptoms of speech slurring started about 4 months ago, and now she is almost impossible for anyone other than me or her daytime caregiver (I still work, as a computer science professor) to understand, and even we are having problems. She has the Tobii Dynavox eyetracking device but has so far not been able to use it easily. Her vital capacity (I forget whether this was forced or slow) has declined precipitously in the last several months; she was in the 90s for a long time, but the latest reading was under 30. We have just started home hospice care.

That is all background to my current question. Since I could not figure out how to start a new thread, I hope someone will react to a blog post. My wife drinks an incredible amount of water. I have not found any explanation of why she is drinking so much water with her ALS, either on-line or by asking her neurologists. Has anyone else experienced this symptom? I have a theory that it is her form of comforting herself, but I have nothing solid to back this up. If it is relevent, she does experience (though she does not always acknowledge the fact) panic attacks, and has refused all psycho-active medications including anxiety medication after a very bad reaction to Zoloft; this is despite entreaties from myself, the doctors, and her daytime caregiver to try them. Her mind is unaffected except for her panic, which I understand has a rational basis; she can do all the puzzles in the NY Times, for example.

If my theory is correct, she takes constant sips of water to calm herself. She has a wonderful device available from Amazon
Fleximug Hands Free Drinking Mug - 24" Straw - highly recommended for all, by the way-
which allows her to drink by herself in the wheelchair. When she is being dressed or taking a shower, she pleads for water every 30 seconds or so, and wakes up many times a night taking several large drinks of water every time she does so.

This would not be a problem, except that she spends her day drenched. Despite a towel and a plastic apron attached by a napkin holder, she dribbles while drinking and her shirt is often soaked. Since she is afraid to use the bathroom, she eventually drenches her diaper and pants, and resists my recommendation of periodic bathroom trips. The bed is completely soaked by the end of the night (the mattress is encased with plastic to avoid more serious consequences). It cannot be good for her to be wet all the time, either physically with potentially fatal diseases like pneumonia, or psychologically, and she often complains of being cold.

Any other experiences of the problem, explanations, or recommendations would be greatly appreciated.