Why does my mum hate everyone?

recently my mum has started to find fault in everyone, friends, family members, and her boyfriend tho they recently split for the millionth time. when she comes to visit shes always dark and moody, and annoyed by someone who 'hurt' her feelings or 'gave her a look' or 'said something condescending" or "dominated the conversatiojn", i dont know whether maybe she was like this always perhaps now im older and with a child of my own, im finding it too much to bear. she unhappy all the time. if i try and encourage her to talk to someone about this, or get the doc to sort out her hormones (they have given her problems in the past) she just scoffs at these 'so called professionals" or if she does see them she fights with them. she is 60, christmas is coming, im starting to dread it as im having everyone over to our house ( me my daughter and boyfriend ). he has been so patient with her moods when she pops by. its making me very angry, i just want my mum back, not this stubborn negative self pitying lady i dont hardly recognise. one of my sisters has turned her back cos she cant deal with her. they both keep bitching to me about eachother, even when i tell them to stop, i know its still in their thoughts. how can this mess be fixed?