AmberI have a 5 week old daughter with CAH. For your neices child to have CAH her and her partner would have to get tested to see if either of them are carriers. It takes both parents to be carriers of CAH for their child to have CAH. Obviously one of your parents is a carrier so that means your brother is probably also a carrier, which in turn means he probably pased it onto his daughter.
the odds are for your neice to have a child with CAH is around 1:15,000. Thats IF she’s a carrier. Some couples have a child with CAH and have another child without CAH.