Gypsies, Shires and Clydesdales are considered 'feathered' breeds. All others are not. Certainly some breeds have tufts of hair, but not enough to be considered a true feathered breed. Mostly, it is just enough to make them look a bit untidy, but not full feathering as the breeds I mentioned.
Nobody can "make" feather. It is a recessive gene. Not easily aquired or kept. Breeding a feathered breed - ie. A Gypsy Horse, Shire or Clydesdale (Friesians are NOT a feathered breed) to a non feathered breed, will not get you a fully feathered offspring. The offspring is likely to have some, but not be fully feathered. Even when breeding two heavily feathered parents, offspring do not always have the feather we would like to see.
Can you post pics of your wife's horse maybe? Maybe we could tell a little about the breed.