First off, I'm so sorry you're going through this.
We can work so hard at our business and one day everything can just seem to go to hell.
I would definitely consult with an attorney and I would also take screenshots of her Facebook post. You may not need it but just to keep it on file. It sounds like you covered your bases concerning the accident, which is great so, for now, I would just stay quiet and keep your ducks in a row. If anything comes of it and Mom decides to push it farther, a lawyer will be able to guide you best. Good luck to you and I hope you feel better.