Mary got badly jolted, but not enough to scramble the infant Founding Father currently floating around in her belly. The party was understandably ruined.
Predictably, Washington was later attacked by the T-1000 on his 12th birthday.
If she'd been sitting a little closer, if her chair had been a little better at conducting electricity, if any one of a million variables played out the other way... no USA.
We don't think we're exaggerating, either. An American Revolution without George Washington--and an early America without him as president-- would have made this whole operation infinitely more difficult. Especially considering historian David McCullough described the Revolution as a near-failure on its own, and Washington biographer Thomas Fleming mused than an American Revolution commanded by Major General Horatio Gates instead of Washington would have "ended in a whimper."