Student or Learner
"A week ago she was reserved. Now she is open. This is a game changer."
"A game changer"= something totally different?
A "game changer" is something that dramatically changes the way people do things. In a literal sense, modern tennis racquets were "game changers" because they changed the way people play tennis.
It is often used in business - the internet was a game changer for business, for example. Most businesses had to change the way they operated.
The TV show "The Simpsons" was a game changer - it reminded people that cartoons could be both intelligent and funny, and still appeal to all ages.