I'm going to call it... it'd be greaaat if I'm wrong, but... the "heroine" is her friend, the programmer.
Can't imagine her coding a "Rebirth" into the game for no reason, and giving it to FMC without testing it.
The fact that she is celebrating her birthday with a discounted piece of cake, hurts right in the meow meow. That thing is basically few hours away from garbage bin...