Hi Leftright:
Welcome!I'm sorry about your difficult situation with your friend.
She’s made 2 suicide attempts in the last 5 years, and so I don’t know what to do.
If you become aware of an immediate & possibly credible suicide threat, you need to call police so they can do a welfare check and possibly put her on a psychiatric hold.
Has she had therapy, meds, in-patient care, etc., after her suicide attempts?
Some people use suicide threats as a form of manipulation, by saying things like, "if you do or don't do certain things they want, that they will commit suicide". Be careful to NOT get caught up in that particular manipulation.
You can encourage someone to get professional help (therapy, meds, etc.), but you can't make them get help. You can't fix them.
She is estranged from her entire family and I’m about the only person in the world who hasn’t abandoned her.
Unfortunately, when some people won't or can't take their mental health problems seriously & make an earnest effort to deal with their problems, emotionally healthy people will set and enforce boundaries that might sound like abandonment to some who don't know the true story (from their prospective). You don't know what you don't know about situations with her family. If you go to the board for those with parents & siblings with BPD (or strong BPD traits), or the board for those with children with BPD, you will read about people who have had to either limit contact or go no contact with the person in their life with BPD.
My best friend has BPD and I’m the only family she has
What's your definition of "best friend"? Is it a healthy definition?
For me, a "best friend" is someone with whom you have a mutually beneficial relationship. You have mutual respect and one can turn to the other during times of need. It isn't a one-way street & it isn't a case where one person repeatedly rescues the other.
Should I let her go, since I feel like I’m doing more harm than good for her at this point, do I beg her to stay, and give in to everything she wants and has been putting me through, or do I try to get her to stay while trying to set boundaries I can live with (which has never worked in the past). I’m at a loss
Only you can decide what's best for you. No one can be responsible for rescuing another, especially if they won't recognize and deal with their mental health issues.
Everyone needs boundaries. Boundaries are things that you have control over and have to personally enforce. They aren't something that you get others to buy into or can expect them to honor.
i.e. If she is verbally abusive to you, you have no power to make her stop. What you do have power over is to terminate a phone call, leave her presence, etc., when she becomes abusive. You merely announce something like, "I can tell you are having a bad day, I'll let you go now (or leave now). We can talk/or I'll see you at a later time"
When she is in an abusive state, you do need to be careful, as some people with BPD will make false reports to police of physical abuse to them.