I had a mom that was very negative - i would describe her as 'toxic' - she would answer the phone at noon with 'you'd better have a damn good reason for waking me up!' - like i knew she was sleeping in the middle of the afternoon...
she was cranky all the time, would snap at people and oh boy - look out if she got a telemarketer calling! And did I mention she the foul mouth to rival any sailor?
Talk to her... try to get her to see how she's behaving, and how she is pushing people away, probe a little and find out why she's so upset about everything, all the time.
And lastly, don't give up on her... she is your mother, and she may be taken from you too soon. I lost my mother a few years ago - we had not spoken for over a year when I found out she was in the hospital and had little time left. I was thankfully able to have the chance to tell her how much I loved her and say sorry. I wish I'd had that year back to spend with her... I have since had to go thru major life changes, without her and it's very difficult... i wish I had her back, even at her worst.