I don't know if this is relevant, but I know from personal experience that some people turn really nasty when stressed and overtired - although my experience is opposite situations - I was really stressed before i had DD and was a real task master at home and would swear and carry on about everything DH did and when my family came to visit I would stress and order them around in regards to keeping my house tidy and not putting things in certain places, and maintaining perfection (a lot unrealistic with a house full, i know, but i think being over-the-top in control of cleaning my house is how i cope with extreme stress). Then, when DD was born, i wasn't working full time (was on leave), couldn't continue on house renovations due to caesarean, and although i was more sleep-deprived, i actually relaxed and the nastiness suddenly left me. The stresses of earlier are not part of my life now, although i am working 4 days a week and have a 2 1/2 year old, but it sounds to me like it is the stress of caring for a baby that is sending your friend nasty.
I would urge you to please look at this as 'how is my friend being affected?' more than how you yourself are affected. It appears that these are symptoms of a deeper struggle with your friend, and the right support should be able to help her move through this if she is willing to take the help.