If you marry an illegal alien what will it take to make her a citizen?

If she entered the US illegaly (snuck in) she will not be able to become legal without leaving. Once she leaves the 10 year bar will be triggered, meaning she will not be able to come back for 10 years. In order for her to come back, her US citizen husband would need to apply for a waiver of the 10 year bar. He would have to prove that it would be an exreme hardship for him to move to her country. It is difficult to get this waiver.

She would not be able to become a US citizen until 3 years after receiving her permanent residence. You can find a lot of information about the waiver that the husband would need to file to overcome the 10 year bar at http://immigrate2us.net The waiver is called the I-601