The maximum period of stay your mom would be granted is six months. Your mom cannot enter the United States with a tourist visa if her intent is to remain and seek permanent residence. Such conduct can be considered material misrepresentation, which makes your mother permanently ineligible for permanent residence without a waiver. You could minimize the period of separation by filing the Form I-130 after she arrives. Filing before she arrives can lead to her being denied admission and subjected to expedited removal. Your mother can stay the maximum time authorized and depart in s timely manner. You can read more about family immigration at http://myattorneyusa.com/family-immigration.
Answered on Jun 09th, 2016 at 1:56 PM