Welcome angelene: I'm so sorry about the difficulty you are having with your sister.  :)oes she live on her own or with your mom/parents? Has she ever attempted suicide? It is important to take threats seriously and in some situations, it may be necessary to call emergency services. Other times, some people with BPD can be emotionally abusive and make threats for attention.
It has to be very distressing for you. It could be helpful for you to come up with a strategy and a Safety Plan to use with your sister. In extreme situations, you may need to have a plan on who to call. Since your sister is in another state, it may be your mom or another relative. As indicated and as possible, it might involve calling emergency services.
When it is clear to you that your sister is trying to manipulate you and being emotionally abusive to you, it would be beneficial to you to have some things prepared to say. You can't be held responsible for your sister and for her choices. The links below lead to two articles that address this issue. You can adapt some of the suggested verbiage to apply to your situation (rather than a romantic partner).
WHEN YOU ARE MANIPULATED BY SUICIDE THREATS WHEN SOMEONE THREATENS SUICIDE SUICIDE IDEATION IN OTHERSThe Safety First link will help you with a Safety Plan. You can feel more confident regarding how you will handle situations with your sister, if you make a plan.
SAFETY FIRSTIt can be helpful for your sister to contact suicide prevention hotlines for support to prevent suicide. They can be a resource for you as well. When you are unsure on how to handle your sister, it can be helpful to talk to someone on the phone. They can be there to assist you and help guide you. The first two Resources below are for the US and the third one is for International Resources. You may want to share this information with your sister.
SUICIDE PREVENTIONTEXT CRISIS LINEINTERNATIONAL SUICIDE RESOURCESIt could, also, be helpful for you to set some
BOUNDARIES with your sister. Boundaries are for your protection and welfare. They could include setting restrictions on phone calls, texts, emails, social media, etc. They are up to you to set and consistently enforce. Your sister won't like your boundaries or agree with them, but they can help reduce your stress and frustration
Hope some of this information help you. Keep in touch and let us know how it goals.
Take care.