Really interesting thread. After years of different interaction with a variety of people in myriad work situations, the biggest question that now always pops into my head is this- Is this someone who is happier being unhappy than they are trying to fix their situation? All else stems from that for me. If they seem to ignore any helpful suggestions and/or observations, then it's likely that they may get some kind of subconscious satisfaction from their negativity. This is a sad condition for them, but can be unbearable for anyone who has to work around them.
If you can, and are prepared to deal with whatever comes rolling back your way...you can follow some of the ideas listed in this thread. But if you see that there is something in this person that is really more about spreading their own state of unhappiness, then you need to find a way of distancing yourself from her. Setting boundries in a work situation are worth it if you're there for the long haul. Good luck!..xx..e