Haven’t seen the show, but....certain types of CAH such as 17-Hydroxylase Deficiency (what Kathy has) CAN make a genetic male (someone with XY chromosomes) look female on the outside. The way I understand it:

The development of the testes is dependent on possession of a "Y" chromosome...what you find in a genetic male. But, the development of the EXTERNAL genitalia is dependent on the presence of male hormones, including testosterone.

Up till about the 7th week of gestation, the genitals of boys (those with XY chromosomes) and girls (those with XX chromosomes) look pretty much the same. But, if a baby makes a lot of testosterone, the genitals will devleop into those of a boy. If there is NOT a lot of testosterone, then the genitals will develop into those of a girl.

People with CAH caused by 17-hydroxylase deficiency make too LITTLE testosterone. That is why an XY person with 17-OH deficiency will have testes, but external reproductive organs that look female. I think 17-OH deficiency accounts for less than 1% of all CAH cases.