I am a graduate student in USA from Bangladesh and my wife is now at Bangladesh. She got the F2 visa, 5 months ago, at the same time when I got the F1 visa. Now she is planing to come to USA as F2 by the end of January 2015. She has the intention to get enrolled here for graduate studies. Is there any limitation that she needs to stay at least few months before applying to change her status from F2 to F1?