CIMT is purely an immigration determination. If you feel harassed by her you can report the threats to local police and ask for an order of protection if you want her to leave you alone. Do consider the implications on others before you act. You probably don't want to alienate your husband's children who apparently are on good terms with her. Perhaps a good talk with them or even her about your boundaries and concerns would be in order before you seek legal action which may adversely affect YOUR relationship with the stepchildren.
This advice does not form an attorney-client relationship and is merely informative. It should not by itself be relied upon to address a legal concern.
I am sorry to tell you that, but you have piled up a bunch of legal words in a context where they do not fit.
NYC EXPERIENCED IMMIGRATION ATTORNEYS www.myattorneyusa.com; email: firstname.lastname@example.org; Phone: (866) 456-8654; Fax: 212-964-0440; Cell: 212-202-0325. The information contained in this answer is provided for informational purposes only, and should not be construed as legal advice on any subject matter.