After turning Laurie's marriage proposal down, it seems as if Jo has confirmed her independence. That act did come with a price though. It also seems as if Jo is destined to live a single, solitary life and never marry. The depressed feelings continue as Laurie leaves and Beth also dies.
I would consider all of the above the climax to the novel. From there, a novel will move into the denouement. I haven't seen a student use that word in quite some time, so I'm proud of you for knowing that it means falling action. Most teachers that I know no longer use that term. I would say that the denouement of Little Women follows a few characters. One piece of the story's falling action is what happens to Laurie. After Jo turns him down, he still manages to marry one of the March sisters. He marries Amy. Jo isn't left out of the wedding game either. She realizes that she isn't going to die a spinster, because she realizes her true feelings for Professor Bhaer. Their conversations are comical and full of miscommunication, but they both eventually manage to convey their true feelings to each other and get engaged.
From that point, I feel that everything else that happens is firmly final resolution. Jo and Professor Bhaer get married, she inherits a mansion, and starts a boarding school.