This is my first time posting here, but wanted to ask for some advice.

My mom has BPD - she was diagnosed years ago, but refuses treatment. We always knew growing up that she had a mental illness. It came in waves, and we often found that the slightest thing would trigger it. She had 3 children, and our father vanished when we were 9, 3, and 1 (I have two sisters.) Obviously our childhood wasn't very normal - we spent many days wondering why other people's parents had seemingly normal day-to-day lives and relationships. She argued with other parents, she found reasons to start fights with our neighbors, and we constantly felt like we were in the middle of strange arguments with family members that didn't really involve us.

Now that we're older (I'm turning 29, my older sister 35, and my younger sister 27) we've grown accustomed to her mood swings and irrational behaviors. She goes to therapy for 3 months at a time, finds a reason to hate her therapist, stops going. She finds a psychologist 6 months later, gets prescribed medication, gets the script filled, and then won't take it because she fears dying.

I live in New York City, and have a very distant relationship with my mother since moving here about 4 years ago. I try my hardest to sympathize with her disorder, but the older I get, the less I feel sorry for her. I don't want to feel this way. I can't stand that she refuses to stick to any treatment, and that she is comfortable with her children suffering through the constant obsessive behaviors and erratic tendencies. 

My youngest sister is the one I am most concerned about in this equation. She is smart, funny, and well rounded, but definitely has some anxiety problems. She's married, has two beautiful children, and she and her husband are saving to buy a house right now. My mother preys on my sister - she knows that she is the sweetest, most concerned, and easily swayed when it comes to family. She forces herself into my sister's marriage, coming over to her house unannounced, critiquing her parenting skills, telling her she works too much, going through her things, asking her about her husband's female coworkers, telling her she's too skinny or unhealthy, telling her she's lonely and suicidal, and so much more. I fear that this constant wedge in my sister's relationship will ruin an otherwise healthy marriage. At 27, they do not need a mother forcing their opinions and thoughts so heavily on them. I know they're young, but they're pretty awesome people who make great decisions for their children.

I had a talk with my sister today, and told her how I felt, and that I think her relationship with my mother is too codependent. She agrees, but we started arguing, because obviously it's easy for me to tell her what to do from a far - she's the one who has to deal with it on a regular basis. It has gotten so bad that about 2 weeks ago, an argument over my sister's new job for a non-profit (my mother watches her children when she works in the office, she works half of the week from home), turned physical. We grew up with her outbursts ending in a slap across the face or throwing an object at us, but to be almost 30 and feeling like your mother can snap on a dime and attempt to hit you is really over the edge.

I want my mom to be healthy, but I really feel that she is too far gone. She's 57 in December, and constantly complains about how her life didn't turn out as expected it would. That nothing makes her happy, that her children don't love her, that she hates her relationship (a guy who has given her basically anything she has ever wanted for the last 9 years but yet she can't stand him), that her children work too much, that her children are unhealthy. We're judged incessantly, we're always wrong, and we are never the right weight. 3 women who feel completely insecure and anxious constantly because of someone else's disorder - when we are all really hardworking, smart people, who try to be as decent as we can be.

Any advice here would be great - I appreciate you reading.

Thank you.