If she said that, then that has to be one of the stupidest comments ever uttered.
Why? Terrorism - essentially the wanton murder en masse of innocents is inherent in the Muslim concept of jihad. Islam is the only religion extant that makes the murder of 'infidels' (non-Muslims) and especially Jews a solemn part of it's doctrine, thus justifying the killing of innocents that, in many cases, are also Muslims. It is a barbaric religion and it's victims corpses from around the world are piled up to the heavens while the murderers continue to terrorize the world with shouts of "Allahu Akbar" yet Ann Coulter's comment is 'stupid'? I don't think so.
If Ann Coulter thinks that every terrorist has been a Muslim, the women is an idiot.
How long has terrorism existed?. Answer: a century, give or take. How many terrorists have been Muslim?. Answer: some.
There have been thousands of terrorists, dozens of groups, thousands killed and maimed, all by terrorists whose ideology is not Muslim. In many cases not even religious.
So how can anyone with ANY knowledge of terrorism, of history, of the modern world, say that most terrorists have been Muslim?.