^ Wasn't gonna start saying much, but since you brought it up, I'm also confused and disappointed about her non-appearance.
Apparently she's still in town so not sure as to why she wouldn't/couldn't make it, especially, like you said, being an ambassador for the brand. Really.
Obviously there are other factors: she's probably precoccupied or simply she was't invited - if it's the latter, that is indeed strange.
It was more understandable that she missed the Pre-Fall show knowing she's in another continent and busy at the same time.
And don't think none of us expect her to show up at EVERY Chanel event, not realistic for her, but particularly this one for sure (and she's done back-to-back couture shows the past years).
With all that said and considered. Perhaps she was just there specifically for Schiaparelli and that's that. Not the end of the world.