@Everblaster
Original Japanese is アイツ, which can be translated as either that man or that woman or even that thing, heavily depending on the context. This is kind of an awakward situation where the most appropriate word should be that thing, as uncle knows that Lumbi is an object and Ayumu doesn't.
It would be rather weird to translate to "that thing", cuz then it would be obvious to Ayumu that Lumbi is clearly not a woman. Yet it would be also weird to translate as girl, cuz i don't know anyone who calls their sweeping robot " a she".
But I do think your suggestion is the best option as some comprimises have to be made, so thanks for pointing that out.