Without the information she may present an assessment of her presentation cannot be made. The decision will be by CIS based on the filing and the evidence presented. You may want to speak with a domestic relations attorney and immigration attorney.
Attorney Robert Brown's (former INS Director, 1972-99) reply to your question is general in nature, and does not constitute legal advice as all facts are known to him. For specific advice or representation you should retain an attorney experienced in immigration law. Mr. Brown's reply on AVVO does not create an attorney/client relationship not constitute legal advice.
Current viability of marriage is not a basis for a denial of the I-751 petition. As a result, if a couple is separated and/or the marriage is not currently viable, your wife still should be able to file and have approved a joint petition, so long as no divorce or annulment proceedings have commenced, and you co-signs the I-751 and appear at any scheduled interview. If you will get divorced or will not show up for an interview, she will have to request for the joint petition be converted to waiver petition based on the applicable waiver ground such as good faith marriage that ended in a divorce. She will be required to produce divorce decree and evidence to show that your marriage was in fact "real".
The information presented at this site is for general information only and should not be constructed to be formal legal advice nor the formation of attorney/client relationship.
You are asking for a detailed consultation not general information. You can do that on a consultation with an immigration attorney. As of now, AVVO is not a law office and cannot offer particularized advice.
The information contained in this answer is provided for informational purposes only, and should not be construed as legal advice on any subject matter,not should it be viewed as establishing an attorney client relationship of any kind.
The best thing you can do for her (either way) is to encourage her to engage an experienced immigration attorney to help both of you sort through what USCIS needs. Although you may be hurt, I am sure you don't want to lie to USCIS just to get her in trouble. If you are not living together, then whether or not you go to the interview, the current I-751 will be denied (or postponed while the two of you get divorced). If/when you get divorced, she can file a new I-751 requesting one of two waivers. Your help and cooperation will be an enormous advantage to her. Best possible world for her is if you go to interview, attest that your both intended to build a life together on the day you married, but you grew apart and you separated. Best to use a good attorney with experience in these post-separation I-751's. We did so complete a job last summer on one that the I-751 was approved without an interview.
You should always consult with an experienced immigration attorney to make certain that the advice you received is appropriate for your particular immigration case.