I just went through a two year battle to get all my medicare squared away. What the lady told your wife is correct with the caveat that I was not a federal employee. If there is any lapse in your qualified insurance coverage you will pay a penalty for part B for the rest of your life. Also, you cannot get any supplemental coverage until you are accepted into Medicare B. Once you are accepted into part B, you can buy your supplemental and your prescription coverage but not until.
Again, this information is based on not being an ex-federal employee. Could be different but I don't think so. The only exception I read about is ex-railroad employees who are covered by their own medical plan.