Barrett sniper rifles were marketed to the military, for their ability to cripple aircraft at distance with precision fire while the aircraft were on the ground, as Watts would know if she weren’t so blindingly ignorant about both firearms and aircraft.
Barrett never asserted that their .50 BMG rifles were useful for firing at planes in the sky.
The Barrett M82 (now M107) was marketed as an anti-material rifle for it’s ability to take out thin-skinned targets such as the engines or avionics of aircraft on the ground at greater stand-off distances than some rifle platforms in use at that time. It was the additional stand-off distance that was key for military use; aircraft are made of thin and light alloys, and the skin of any commercial aircraft can readily be penetrated with any centerfire rifle or pistol bullet.
Once again, Watts is using the ignorance of her followers to manufacture fear.