Really??? Sounds like that cop was having a bad day...
If that was here, I would go fight it in court. It should only cost you a few hours, and if the cop doesn't show, the ticket is almost always thrown out. Even if he does show, simply stating that it was not safe for her to change lanes should get it thrown anyway. Difficult to prove either way, but the judge should side with your wife, unless the cop has dashcam footage or some irrefutable evidence.
Of course, I Am Not A Lawyer, but I've had a ticket or two thrown out for the same reason.