Classic/favorite Spanish novels?

My mom has been learning Spanish for several years now and will soon spend several months as a music teacher in Bolivia (!) She got a new ebook-reader for the trip and LB and I want to get her some novels to read in Spanish. I know very little about Spanish/South American literature, so recommendations would be very helpful. A friend already recommended Frederico Garcia Lorca and Isabele Allende and "that one author whose names escapes me right now but I'll tell you later", but not specific works.