Give your player a variable that tells which direction he should be shooting based on input and/or direction.
Player is facing right (not mirrored)? Set variable to 0
Player is facing left (mirrored)? Set variable to 180
User is holding up? Set variable to 270
User is holding down? Set variable to 90
Then when the player shoots, create the bullet and set its angle to the variable. Of course there's a bit more to it but you get the idea o.o