Simple Mendelian genetics monohybrid question?

So looking at the pedigree, you can ume the parents didn't have CF (its not mentioned) but you can deduce that they both must be carriers, since they had a son with CF. Now since they have genotypes Aa X Aa, 1/4 of their kids will have CF (aa), 1/2 of their kids will be carriers, but outwardly normal (Aa) and 1/4 of their kids will be non-carriers and completely normal (AA). Now, we know Kathy doesn't have CF, so she's either AA or Aa. This means there's a 2/3 chance that she's Aa and a 1/3 chance she's AA. Now since her husband has no family history, it can be umed he is not a carrier, so he's AA. Now, if Kathy was a carrier Aa, then when they have kids (AA X Aa), 1/2 of them will be carriers, 1/2 won't. So altogether, the likelihood is 2/3 X 1/2