On my last visit to USA, there was an aunty (not my family memmber, just stayed on same street with her dad in Nigeria sometime back) who accomodated me in her home throughout my stay, she offered me accomodation and feeding. Now, I will be going again to USA and will stay in her home. What is a good gift that I could buy for her or her family from here? Please note that she has 4 kids (2 girls, 2 guys).

buy then food stuff from Nigeria that you can get past customs. By her kids things that children in Nigeria love snacks wise. or maybe help out by giving her money for groceries when you get to their home.