回复：Urgent H4 visa

from my understanding that your wife has to come to USA before the old i797 expired. The h4 visa expiration date is the same as your i797 (the old one). If she can't make it, her visa will be invalid and everything has to start over. In that case, no doubt that your wife should bring your old i797. The other reason for your wife to come earlier is that her H4 visa requires to extend soonest possible, otherwise she will be out of status soon.