How do I deal with my 90 year old mother who is so nasty, spiteful and vindictive toward me I now have high blood pressure?

My mother is almost 90 and still lives independantly and has Home Care for an hour a week.

I am in Australia.

She is so nasty, rude, vindictive and spiteful toward me but treats my sister and her husband like fairy floss on a stick.

Unbeknowns to my mother they have lied on many occasions to her in regards to her Aged Care package to the point where my name had been taken off the package ( I and my sister are her Power of Attorney etc).

She does not have dementia and its now at the stage where our only son does not call her as she has made comments to him about me which is cruel for him.

He refuses to tell me what she has said.

I am becoming physically ill and I have suffered depression before and got through it without medication but she is really bringing me down.

My other sister and her husband are typical Narcissists and I have called them out before for their lies and deceipt and I am now at the stage where I feel my mother should be told what they did behind her back with her package.

My husband (who is amazingly supportive but very angry at how I am being treated) lost his mother when he was 3 so it cuts him deeply to see her treating me like she does.

She constantly insults me, pulls faces at me and even said to my sister when I went out to bring her washing in last week (Thinking I would not hear her) "Where has the little bitch gone this time" WOW! Its not the first time she has name called me and this time I walked straight into her lounge room and made it quite clear I heard her by responding with. " I was getting your washing in for you Mum while you and $$#** were sitting there discussing me." I lost it a tad yesterday as 3 times I said to her "OK Mum I will head off if you dont mind so you go and rest if you're not feeling well" (She ignores me when I arrive and say hello and the same when I leave) Yesterday I said to her "Excuse me Mum did you hear me" after the 3rd time and I was standing beside her bed. She then proceeded to turn the tears on and when I said to her "Mum why are you crying" her response was. "Its the way you treat me and speak to me" I just got so frustrated and said to her. "Well what about the way you and &^& $#@ (my sister and her husband who have caused so much trouble in the family AGAIN) treat me. Maybe if I was more like &&%% & %$%$# I would be more popular. I have had enough of this crap and every time I turn around someone is sticking the boot in" I then left slamming the door and again my blood pressure is high. I have a friend who is a retired Nursing Sister and so many supportive not blood family who all tell me the same thing. "Walk away or we will be burying you before your mother" I have 4 siblings and get no support off them at all as my sister and her husband have managed to alienate them all from my mother. I feel that they have a set agenda for Mum and they have worked with aged care all their lives. They patronise her, fuss over her and swathe her with attention. My hubby and I do so much for her and we dont even get a thank you. Hubby says stay away the same as my supportive friends say but when I do stay away for a few days she is worse. She is supplied meals and is well looked after but I am at my whits end.