Too dense. Let's break down the story elements --
1. Kara viciously harassed during an online game
2. Kara befriends her rescuer
3. Kara begins to believe her rescuer has sinister motives
4. Kara must expose him before the game turns fatal
-- and tick of the typical logline elements:
1. Protagonist - Kara
2. Antagonist - Nice Guy
2. Protagonist's internal problem - too meek
3. Protagonist's external problem - she's the only one who knows his sinister plans and, presumably, she needs proof to convince others
4. Stakes and ticking clock - if she doesn't act, the game will turn fatal
5. Conflict - weakly hinted at via "must expose him".
So we've got most of what we need for an effective logline. The story spine -- the path the story will chart -- is "Kara must expose him before the game becomes fatal." That's your story bedrock.
One thing begging for clarification is the game itself. With "the game" undefined we have nothing to frame our expectations. Is this an online MMO? An ARG?
Is this a movie you'd go see?
"A timid gamer girl falls for the man who saved her from vicious online bullies. When she learns he'll use a live-action alternate reality game to kill for real, she must stop him -- and the only way is to play."