I bet that it is impossible to talk to her about seeking counseling when she's emotionally dysregulated. My guess is that it is extremely frustrating for you because you love her and the kids and just want the best for everyone involved. I know that's how I would feel in that situation.
When a pwBPD is in that state, their actions and thoughts are ruled by their emotions. That is a good time to listen with empathy and not invalidate her. Telling her that she's hurting her children (whether true or not) does just that; it invalidates her. But, now that you've told her, let it go unless she asks about it.
There are a lot of great resources on this site to help you improve the relationship. There are initial tools in the sidebar to the right of this page to help get you started. Reading the posts of others, taking a look at the workshops and lessons, and asking any questions that you are comfortable with should also help. We are here to support you.
How long have you two been together?
I look forward to reading more about your story. Keep posting, it's therapeutic!