I became a U.S. conditional resident through marriage to a U.S. citizen. However, I did not turn in my I-751 on time because my husband and I had been going through some difficult times after he lost his mother, and I thought I would just rather go back to my country, Italy.
Everything is good now between us, though, and we applied for the I-751 together even though we were six months late. Now while we wait, I'm worried, because I don't really know what my immigration status in the U.S. is. Am I illegal? Can I be deported? Can I get a job in the U.S. even if we filed late?
According to U.S. immigration law, a person loses permanent resident status automatically after failing to file an I-751 on time. Based on the facts you've described, this is what happened to you, and you immediately began accumulating what's known as "unlawful presence" in the United States.
As a result, it became immediately possible for the U.S. government to legally remove (deport) you.
If you have not yet received an I-797 receipt from USCIS (showing that you filed the Form I-751) and have not received anything by mail from the immigration court, you should call the Executive Office for Immigration Review's case information system to make sure that you have not yet been placed in removal proceedings or been ordered removed. (You will need your "A" number, which you can find on your conditional resident card.)
If you have already been ordered removed, even if this happened without your knowledge, then your I-751 will be denied. In such a situation, you should try to get the immigration judge to reopen your case. This could allow you to file a new I-751, this time in immigration court. An attorney can help you with this.
Otherwise, if and when you receive your I-797 receipt, you should definitely not think of yourself as "illegal" or undocumented, because that receipt (coupled with your expired conditional resident card) would allow you to obtain a Social Security card, to work legally, and to re-enter the U.S. if you chose to travel abroad.
Filing the late I-751 did not completely reinstate your conditional resident status, however, and, if your petition is denied and you must leave the country and then try to return, you might be hit with a three-year ban for the time you spent in the U.S. between the expiration of your resident card and (at least) your actual I-751 filing date.
Whatever happens, do not forget that, regardless of your immigration status, you preserve at all times certain basic constitutional rights (against illegal searches, for example) that all government officers are required to respect. Contact an experienced immigration attorney if you need more information on this subject.