How do you deal with coworkers who thinks they know everything because they've been in the same position for waay too long - probably because they are not capable enough to be promoted?

And how do you cover your butt when she gives you a piece of false info that she would later deny to have given?  Or when she provides instructions that are as clear as mud? And then announce my "mistake" to the whole team?

What do you do about a collaborator that has, time and again, failed to read or to comprehend simple concepts that they are supposed to be familiar with?

I've been pulling my hair too much and I need the long weekend to come soon...