I am Jewish (Middle Eastern/Mizrahi) and black. I sort of understand what the OP is saying. I would say many people mixed with african and caucasian decent do exhibit hair in the type 3 category. Now whether that's a,b,or c.. depends on on genetics.. LOL! I have type 3c hair and the majority of people I notice that are mixed with african and caucasian that wear their hair naturally curly often have type 3c hair but THINK it's 3b and refer to it as such.
Middle Eastern Jews can be a range.. many Jews of ACTUAL Middle Eastern decent often exhibit curly hair falling in the type 3 range of curls whether it be a,b, or c.
So I do comprehend her observation..but I wouldn't say ALL or even the majority of mixed people have type 3b hair at all.. plenty of predominently Caucasian people exhibit 3b hair.