Hi there, and a warm welcome to your friend!
In New York, visitors like your friend can still drive legally, so long as they have a valid license from their home country for the duration of their stay. Still, I'd definitely recommend that they bring along an international permit (if they have one), since this might help in cases where your friend will be stopped by law enforcement. After all, an international permit is basically just an English translation of ther native driver's license.
And remember, make sure to drive safe!