what will happened if my mom didn't do to US for 2 years
from
findlaw:
It is a common misconception that to keep your green card all you need to do is enter the United States at least once a year. The fact is that if you ever leave with the intention of making some other country your permanent home, you give up your U.S. residency when you go. The border officials will look at your behavior for signals that your real place of residence is not the United States.
As a general rule, if you have a green card and leave the United States for more than one year, you may difficulty reentering the country. That is because the U.S. government feels that an absence of longer than one year indicates a possible abandonment of U.S. residence. Even if you do return before one year is up, you may run into trouble. To avoid a full-scale inspection, you should return within six months.
On the other hand, remaining outside the United States for more than one year does not mean you automatically lose your green card. If your absence was intended from the start to be only temporary, you may still keep your permanent resident status. However, you may no longer use your green card as a U.S. entry document. You must have what is known as a reentry permit, or you must apply at a U.S. consulate for a special immigrant visa as a returning resident.
Reentry Permits
Reentry permits are for people who hold green cards and know in advance that they must be outside the United States for more than one year. Under such circumstances, USCIS can allow you to stay away for up to two years. You should send in your application before leaving. Use Form I-131, available on the USCIS website at
http://www.uscis.gov . If approved, a reentry permit will be issued and will serve as an entry document when you are ready to return.
Reentry permits cannot be renewed and can be applied for only inside the United States. If you want to stay away for more than two years, you must return briefly and apply for another reentry permit.
Returning Resident Visas
If you stay outside the United States for more than one year and do not get a reentry permit before leaving, you must apply at a U.S. consulate abroad for a special immigrant visa as a returning resident. You must convince the consular officer that your absence from the United States has been temporary and you never planned to abandon your U.S. residence. You will have to show evidence that you were kept away longer than one year due to unforeseen circumstances. Such evidence might be a letter from a doctor showing that you or a family member had a medical problem. If you do not have a very good reason for failing to return within one year, there is a strong chance you will lose your green card.