At this point i doubt we'll even see BM's other children until the end of the arc.
They fell down the waterfall and even if they all made it back up again, Onigashima is floating and heading for the capital so who even knows if they can get there in time.
Honestly i think BM will end up betraying Kaido when things get uglier for them by nabbing the capital's poneglyph and escaping with her children.
So if we somehow end up having Zoro fight Smoothie it would have to be later, at which point Zoro would pretty much be stronger than her without a doubt.