One of the most important factors when facing this topic is the following: Does the child want to be interacting with their parent? If so, this can be done is a supportive way with all family members on the same page, and I highly suggest involving a mental health professional who has experience in addiction and working with children to help facilitate this process. If the children don’t want to be interacting with their parent at that time, do not force them. If they appear to be suffering from significant distress absolutely get a mental health professional involved with the children.
If possible, let her daughter know that she is not responsible for her mother’s treatment, and check in with her regularly about how she feels about what is going on. Addiction impacts the entire family, and your niece may not have a full understanding of how her actions while under the influence have impacted her children, and the rest of the family.
Hopefully once she gets into a 30 day treatment facility she will begin to understand, and if there is a family program available take advantage of it and attend! You can even ask her children if they’d like to attend (but again, don’t force them if they don’t want to).
I’m curious as to how others have navigated scenarios like this? It’s certainly very difficult and her children are lucky to have you in their lives!