I came to the United States with my mother, after my father petitioned for us. My father was a lawful permanent resident at that time. I knew that I couldn’t bring my girlfriend with me. However, after I got my visa, she was very upset at me leaving, and so the night before my family took the plane to the U.S., she and I secretly got married. No one even asked about it when we entered the United States! But now, it’s a few months later, and of course I want to be able to petition for her to get a green card. Can I do this?
The short answer is “No,” you cannot petition for your wife to come to the U.S. as the spouse of a permanent resident. The reason is worse news yet: You yourself do not appear to be a permanent resident. If you were given a visa as the unmarried child of a lawful permanent resident, then you were legally bound to remain unmarried right through the date that you entered the United States to claim your status as a lawful permanent resident. Marriage invalidates your permanent residency in such a situation.
Apparently no one in the U.S. government has noticed this yet, but filing a petition on your wife’s behalf would likely bring it to their attention. (So would later applying for U.S. citizenship, at which time the U.S. immigration authorities have an opportunity to review your entire file, and will institute removal proceedings if they discover that you were not eligible for your green card in the first place.)
What you should do now is consult with an experienced immigration attorney. There is a chance that your residency can be salvaged or reestablished, but you will likely need to succeed in applying for a waiver (legal forgiveness) of your visa fraud upon entry to the United States. This is not something that can easily be done without professional help.