In X-Men: True Friends (an would-be Excalibur graphic novel series that got downgraded to an X-Men comic, Kitty Pryde goes back in time to 1936 with her "true friend" Rachel Summers (take that, Illyana Rasputin!) Also, she hangs around with the future Queen Elizabeth II! Marvel Team-Up!
Also: she vows to kill Hitler.
Panel from X-Men: True Friends #2 (October 1999), script by Chris Claremont, pencils by Rick Leonardi, inks by Al Williamson and Jimmy Palmiotti, colors by Shannon Blanchard, letters by Tom Orzechowski
Panels from X-Men: True Friends #3 (November 1999), script by Chris Claremont, pencils by Rick Leonardi, inks by Al Williamson, colors by Shannon Blanchard, letters by Tom Orzechowski
But, although Kitty talks a lot about killing Hitler, she never actually does.
I'm pretty sure if there's anyone in the Marvel Universe we'd like to be unsullied by killing Hitler, it's Kitty Pryde. And possibly Squirrel Girl.