When everything is so very exaggerated as it sounds like your partner was expressing, I use humor on myself to get myself to realize how "ridiculous" it is. Taking individual mishaps to extremes is one way ("I'm going to be late to my own funeral") or otherwise mocking that aspect of myself and how I'm making things seem worse than they really are:

Nobody loves me, everybody hates me
Think I'll go and eat worms

http://bussongs.com/songs/nobody_likes_me_worms.php

A really good friend can do the same for me, remind me that it's not quite THAT bad. Be pleasant and "unworried" and tell her she has 5 minutes to grouse and so she better make the most of it.