Okay, so lets say your animation frames for the directions are: 0 - right, 1 - down, 2 - left, 3 - up
right after the bullet is created add an event for the bullet:
Set angle of motion (or bullet angle? not sure here) = 90 * Sprite.AnimationFrame
This way the bullet will go:
Frame 0 -> 90 * 0 = 0, right direction of movement
Frame 1 -> 90 * 1 = 90, down direction of movement
Frame 2 -> 90 * 2 = 180, left direction of movement
Frame 3 -> 90 * 3 = 270, up direction of movement
Hope that helps :)