I caught that too. Before the end credits they show Donnie as Black Mask saying that the Chinese had to resist the Japanese for many years, etc. But when the new Japanese colonel is introduced at the base there is an army woman who looks very much like Qi Shu. But the whole scene is in wide long shot, you can't really see the faces of the Japanese army and that's because it's not really supposed to be a character set-up just a transition to the end mostly.
My guess? They probably shot scenes of the Japanese Army base and all the soldiers standing at attention while an important dignitary visits the base. It could be that Fang Qing/Qi Shu was in that shot but it wasn't meant to signify anything. It wasn't supposed to be in the present narrative the editors just put it in because they had all this extra footage of the Japanese Army and they needed it to pad out the rest of the film.
So Fang Qing wasn't supposed to be alive at the end like in some surprise twist but her actress was in footage they tacked on at the end. At least that's how I'd see it as.
In a big Hollywood film that would be kind of sloppy editing and in a more artsy independent film that might open up thing to interpretation, but this being a Chinese action flick, it's not any of that.