I can definitely see your distinction between "intersecting" and "intertwining," and it helps to clarify what you'd meant.

My guess is that Crenshaw used race and (biological) sex as joint starting-points for her theory of intersectionality because, at that point in time (late-1980s?), race and sex were primarily the only two aspects of people's diversity that were ever significantly celebrated or spotlighted in mainstream media.

Although I don't know Crenshaw personally, I suspect that -- in the contemporary era -- she would support adding new attributes to the intersectional map, wherever relevant.