Hi Liona and welcome to bpdfamily
I understand your concern for your niece, BPD is quite a difficult disorder and it really isn't easy for a child to have a parent with this disorder.
Here is someting I found that she wrote,
Where did you find this letter written by your niece?
I gather from the letter that her mother, your sister, got a counselor at some point. Is your sister still getting counseling? Has she been officially diagnosed with BPD?
I loved my mommy so much and I missed her and for the first time ever I too wanted to die
It is very sad that your niece felt this way. Do you perhaps know if she still struggles with these kinds of negative and/or suicidal thoughts?
To help you talk to your niece, I encourage you to take a look at some of the tools from one of our other boards (Co-Parenting):
Lesson 5: Raising Resilient Kids When a Parent Has BPDWhat to tell kids about a high-conflict co-parentTOOLS: The Power of Validating How Kids FeelTOOLS: Child development and parents with mental illnessTOOLS: Helping our children deal with traumaARTICLE: Typical Reactions of Children to DivorceI hope this helps.
Take care