Correct... Jenny McCrea was killed by Mohawks just before the Battle of Saratoga. In the weeks before, British General "Gentleman Johnny" Burgoyne had issued an edict that he would be, in essence, unleashing England's Mohawk allies on the patriots in Western Mass, Western Connecticut and Eastern New York... This caused outrage among the Patriots and continentals because this was considered a despicable act by the British. Not long before the battle of Saratoga, a group of Mohawk (Wyandot) scouts ambushed and killed Jane McCrea, scalped her and brought her scalp to Burgoyne to claim their bounty. Burgoyne was disgusted, to his credit. But could not punish the Mohawks or risk having all his scouts and fighters go home.
Despite the fact that McCrea was from a Loyalist family, the network of Patriot pamphleteers and newspapers grabbed ahold of the "Jenny McCrea" story. Her name was 'turned into a kids name' specifically to help inflame sensitivities. But the patriots and ran with it, creating utter outrage among the colonists all across New England and New York. An estimated 20,000 men grabbed their muskets and (more importantly) rifles, and headed towards Burgoyne's Army. And they were looking for blood! McCrea was a true martyr... even though her family were loyal to the king!!
Between the infusion of American Colonists, Benedict Arnold's heroics (this was before he turned traitor) and Daniel Morgan's riflemen, the Continental Army had one of its biggest victories at Saratoga. At exactly the right moment. France was waiting for a 'win' to come into the war to help the Continentals. And Saratoga tipped the balance and showed the French King that the Americans could beat the British in a major battle. After Saratoga, Ben Franklin, at the time an envoy to Versailles, was finally given an audience with the king and foreign minister... and was given money, support, weapons and supplies. Without France's entry into the war at this crucial period, England likely could have crushed the Continental Army within the next couple of years.
Jenny McCrea's death, while probably blown way out of proportion in some regards (both at the time and in history) was the major spark that sent an Army out looking for British blood. They got it... Psychological warfare goes back a long way!
Cheers,
Sirhr