Your criminal record does not prevent you from petitioning your fiance for a green card as long as you are a US citizen. It does not matter that her visa exipred if she entered the US lawfully in any status other than K status sponsored by someone else or C status.
You can have a second economic sponsor fill an I-864. Your criminal record has no bearing on the ability to sponsor.
Under the guidelines set by AVVO, this response is general information only and not specific legal advice, and no attorney client relationship is formed by this response to your question.
It depends upon the crime for which you were convicted. If it is one that involves domestic violence, among a list of other violent offenses, then there may be issues based upon the Walsh Act.
The fact that you have not filed a tax return means that you will need what is called a joint sponsor to demonstrate that he or she can support your spouse should you be unable to do so.
You are best served by looking into a not for profit legal services agency that helps those with immigration matters, who are financially challenged. These agencies should have attorneys who supervise. They charge minimal fees, if any. The USCIS Office should have a list of these organizations in your area. Good luck.
This is general information, not legal advice, and does not create an attorney client relationship.