((((tjp)))), IMO we mourn our children because of the loss we feel of what could have been it is a painful process. I at times repeat that process over and over and have to snap myself back. I know how you feel and hope today is a better day for you.
I agree that maybe if you can focus on your son is clean and safe today, and try and stay in today so easy for us to say yet often so hard to do.
My DD and I both have BPD, when she was younger she was much like your DD and is still in some ways. I have been fortunate with my BPD my counseling helped there is hope never give that up.
I have learned that visuals help calm me at times I first learned this when I was diagnosed with panic disorder, took me awhile to be able to get it but I close my eyes and imagine myself on a big rock by the ocean and see the waves and seagulls and it helps me.
Hugs from one mother to another.