Fatima is the girl that almost distracts Santiago from his dream of reaching the pyramids and his treasure. She's so pretty, and he's so in love with her, that he almost decides to just stay at the oasis and take her instead of the treasure. (You know, because women and treasure are pretty much exchangeable. Headdesk.) But he and Fatima have Twu Wuv: she knows that Santiago will be back for her if it's meant to be, so she urges him to continue his journey while she waits patiently at home for him.
She shows up for the first time at the well, where she's the only person at the oasis who's willing to talk about the alchemist. When Santiago sees her, you can imagine some sappy music and light shining down through the clouds:
At that moment, it seemed to him that time stood still, and the Soul of the World surged within him. When he looked in to her dark eyes, and saw that her lips were poised between a laugh and silence, he learned the most important part of the language that all the world spoke—the language that everyone on earth was capable of understanding in their heart. It was love. (2.256)
That's all well and good for Santiago, who's been doing a lot of thinking about the Soul of the World and the universal language on his trek across the desert. But hand on a minute: has anyone thought to ask Fatima about her feelings for Santiago? A few days later, when Santiago sees her at the well, Fatima tells him,
I have been waiting for you here at this oasis for a long time. I have forgotten about my past, about my traditions, and the way in which men of the desert expect women to behave. Ever since I was a child, I have dreamed that the desert would bring me a wonderful present. Now, my present has arrived, and it's you. (2.287)
Flowery language aside, this is the desert equivalent of checking the "Yes" box on a grade-school love note. Fatima shows Santiago not only that she loves him, but that she, too, understands the language of the desert and follows the omens. Except that she's not looking for buried treasure; she was looking for her man.
And notice that, instead of getting jealous or insecure, she tells him that she'll wait for him because she is a "desert woman" who is used to waiting. Fatima, like the Englishman, serves an important purpose in the novel, because she shows the way that real love isn't jealous, and lets the beloved pursue their Personal Legend rather than holding them back or being insecure. (No word yet on whether women get to have Personal Legends of their own.)
One last thing before we go. The way we see it, there are two major religious traditions bubbling away under Fatima's admittedly rather shallow surface.
(1) In the Hebrew Bible, Jacob meets his future wife Rachel at a well, and Jacob is basically the founder of the tribe of Israel.
(2) In Islamic tradition, "Fatima" is the name of the Prophet Muhammad's daughter.
Given all the mystical religious woo surrounding Santiago's name and the other Biblical references, we're pretty sure that we aren't reaching here. But what to make of it? Maybe Coelho is making a comment about the universality of all religions. Maybe he's suggesting that Santiago could be the head of a new nation. Or maybe he's just trying to cover all his bases.