This book doesn't really follow the classic three-plot structure, but we'll give it a try. Act I would be everything that happens to establish our idea of what the farm is like and what Africa and its inhabitants mean to the author. She's irrevocably tied to her mission of growing coffee. This Act is the majority of this decidedly untraditionally plotted book.
When Denys dies, it's the moment when Africa really changes for the author and she realizes there's nothing to hold on to there, and must leave.
Packing up her stuff and selling or giving it away is all that's left for the narrator to do to resolve the text. The wrap-up is her farewell (and also the part of the book that really chokes us up).