She can use any name she wants. That doesn't make it her legal name, however. You should not waste your time consumed with such minutia as what name she is using. Rather, you should be consulting with and retaining an attorney to determine your rights and responsibilities as well as determining how to best legally proceed to protect your own interests.
Responses are for general information purposes only, and are based on the extremely limited facts given. A consultation with an attorney experienced in the area of law(s) indicated in the question is highly recommended. Information and advice given here should not be relied upon for any final action or decision, as the information is limited by its nature to the question asked and the fact(s) presented in that question. THIS RESPONSE DOES NOT CREATE AN ATTORNEY/CLIENT RELATIONSHIP, particularly considering that the names of the parties are unknown.