Bitches, if mated or not, go through a huge hormonal strain after they have their season.Their bodies and minds prepare for puppies and the hormonal system supports this to the nth degree. All bitches that have not been speyed will go through this to a certain degree. In a case as your friend's bitch it is called a false pregnancy. It does not sound like a big deal but to the bitch it is a psychological nightmare. Tell your friend to get the bitch speyed as any other action, such as breeding or leaving her until next time will not cure the problem. Speying is the only thing that will stop his/her bitch feeling so confused in the future.