@Calliopenjo
triggered by a subject earlier on I've been throwing myself head over heels into the study of how to construct a good (=satisfying) story. I found that in the area of scriptwriting, there are strong opinions on how to craft a story that works with audiences. (With the huge budgets involved, they have no choice but to bring it to something of a formula). While there is dispute about the rigidness of that approach, many (including myself now) seem to agree on the basic elements that need to be present in a story in order for it to be liked by a larger audience. Therefore a lot of novel writer also read the books and take the classes of Vogler, Truby, Kin, Snyder and others to learn on the elements and plot points of a good story.
Based on my findings I would say: its not so much about what kind of ending but if it is true to the inner and outer story arc you have developed over the course of the book. In the beginning of most successful movies (and as far as I have found in my research, an astounding amount of successful books as well), you establish two story lines an "inner story" (the character development), and an "outer story" (something that actually happens, the main protagonist doing something fascinating or cool). In good films or books, these two are somehow related. An interesting example that adheres to that principle, even though you wouldn't expect it is the Indiana Jones film where Indy meets his father. Right at the beginning, while the outer story is established (him fighting the Nazis etc), the inner story line is set up (him not being able to forgive his father). Throughout the entire film Indy eventually learns to forgive his father and rebond with him. A vital element to close that development arc at the end is to setup an achievable element at the beginning. For example: for Wall-E, the main goal is not to win Eve's love, but to hold her hand. At the end, he achieves that goal and the audience is satisfied.
Your ending should fit to the inner and outer conflicts you have established. And then, at the end she should achieve her beginning goal. Maybe at the beginning you made her write a diary in which she confesses that she is lonely, in spite all the money and desperately longs for a true friend. In her adventures, she finally finds one (male or female, doesn't matter,), but that friend turns out to be gay. Maybe she even discovers she is gay herself? The idea of "going through mirrors" throughout the book is a nice "outer arc" story echoing the theme of internal transition. Which side of the mirror is the "right" one?). If she dies at the late end of the book it is then still a satisfying ending, because you have closed the inner arc and shown her reach her initially stated goal (find a friend), and change (transform to an open minded person). Even if you never mention that diary ever again throughout the entire story, even if she dies and the last chapter shows the diary getting thrown into the trash, or lies in the street, and the wind opens it to the confession page (where it is read by another girls walking by etc) it is still a satisfying (and nicely sad) conclusion, because she reached her goal before she died and her sprit (and the books spirit), come to a rest.