question about the girl singing the song and maggie crying scene

There's a lot about this movie that's open to interpretation, but in my opinion the crying was a response to a lot of things. The girl onstage starts her song just as all the kids dash out for the pony ride, but she still performs for her audience of one, singing with a ton of heart but no talent whatsoever. That's poignant enough all by itself, but then Emme's just seen her mostly-eaten cake, driving home the point that she works so hard to create something that's so transient and frivolous. Then the lyrics, "Your love is better than ice cream", which may make her think of her largely loveless marriage (she and her husband talk past each other most of the time, each apparently having a conversation with himself, but not really conversing with each other). And cake and ice cream go together, once again reinforcing the frivolous and decorative nature of her career. Then comes the chorus, "It's a long way down..." with the idea that all her striving in business has brought her to a level of success, but it could all be gone tomorrow. I'm sure at this point, she's thinking of her competitor/friend who committed suicide. We don't really know why, but the timing suggests it might have been because she lost this very client to Emme; this is the party where she's serving "The Rosalind," the cake that beat out Sefara's ganache. And in keeping with the undertone of 9/11, she probably also has in the back of her mind other ways it can all disappear -- being suddenly presented with the choice of dying in flaming jet fuel, or diving a thousand feet to the sidewalk.