Originally Posted by aguilan

Your sister won't start accruing illegal presence until she's 18 and 1/2 years old. If she leaves on the day after she turns 18 and 1/2, she'll face the three-year-ban. Stay until she's a day over 19 and she gets the 10-year-ban.

Leaving before she's 19 and then returning on a non-immigrant visa isn't impossible, BUT she may have problems obtaining said visa. She will have to demonstrate that she will to return to her country of origin after she finishes her studies. Proving ties to her country of origin is going to be difficult especially if you and your parents are still in the US.

If your sister were younger I'd recommend having one of your USC relatives to adopt her so that she can citizenship ASAP, but as is she's almost 16. I'm not too well-informed about the adoption process, so here's a thread about adoption by a USC http://dreamact.info/forum/showthrea...light=adoption