My grandmother's visa expires two months before the admit until date on her I-94. Does she have to leave before her visa expires, or can she leave without any problems securing a visa in the future, a week before her I-94 admit until date?
US visas do not have to be valid throughout your stay, they only have to be valid when you request entry on the Port. After that only your I-94 dictates until when can you stay in status. If your visa expires while you are in the US it does not cause any problems.