I believe you asked this question over the weekend, and were provided answers. Please see the link below.
It is far riskier for your sister to lie on the N-400 application than to state the truth regarding her husband.
This information is provided as a courtesy based upon the limited information provided in your post and does not constitute an attorney-client relationship.
There is no way to promise that they won't get in trouble
But, she has no choice, she must tell the truth on the form.
Most officers don't ask about the spouse .... but it could happen.
Meeting with an attorney would be a very wise thing to do.
PROFESSOR OF IMMIGRATION LAW for over 10 years -- This blog posting is offered for informational purposes only. It does not constitute an attorney-client relationship. Also, keep in mind that this is an INTERNET BLOG. You should not rely on anything you read here to make decisions which impact on your life. Meet with an attorney, via Skype, or in person, to obtain competent personal and professional guidance.
She should answer all inquiries truthfully on the N-400 form, as she will be questioned regarding the application under oath at the interview. If she is concerned about her husband's status, she really should consider consulting with an immigration attorney prior to filing the application to avoid any problems.