Though I should say that do not practice in Washington, your state appears to be among the jurisdictions recognizing a criminal complaint against actions constituting computer trespass. You may contact your local law enforcement authorities for instruction regarding how to file a complaint in your area.
Depending on a number of other factors, there may be other methods by which you can effect a take-down of your son's facebook page (DMCA, etc.), and to that end I would suggest you contact an intellectual property attorney in your area to discuss your options.
This is definitely a violation of Facebook's policies and your son shoudl report this rigth away to them so they delete HER account, or at least restore his access to his account.
I'm only licensed in CA. Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
RCW 9A.52.110 - 130 address the crimes associated with Computer Trespass. You should probably contact facebook. You may also have a cause of action at civil law. you should probably speak with an attorney.
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