Very interesting theory, but since she was just shot in the back in the latest episode without much attention being paid to it… I’m inclined to believe she’s just an Imperial officer.
I just re-watched the scene were they take the bridge and I couldn’t see her in it, though it is a bit hard to make out faces some times. However, there’s no clear shot of her being killed.
I personally think it’s a bit of an odd casting for Sabine anyway, so probably just a SW fan casting (like Paul Sun-Hyung Lee), though it could work, and it would be a fun way of sneaking the character into live-action.