She only had a knife?  
Oh, wait. Jeremy Christian only had a knife and managed to kill two men and wound a third in Portland.
Khalid Masood Fatally stabbed an unarmed office in the Westminster attack.
Richard Stull stabbed Kathy Braun to death.
Knives are deadly weapons.
PSA from Jaded: Do not threaten a police officer (at all) with a knife. It could be fatal.