Stop using the words "left" and "right" or "up" and "down". You're confusing yourself thinking about "right" hand or "left" hand. In mirror you's world, those words have different meanings.
Instead, put a paper bag on one hand and stick your hands out. Look in the mirror. Your "bag" hand and mirror you's "bag" hand are both pointing the same way!
Now stick the bag on your foot. Look, mirror you's bag foot and your bag foot both point the same way!
Now stick the bag on your head. Look, mirror you's bag head is in the dark!
But seriously, everything in the mirror is oriented congruently with this "side" of the glass. The appendages wearing a bag always match up. "Bag hand" and "not bag hand" match just like head and feet do.
Instead, put a paper bag on one hand and stick your hands out. Look in the mirror. Your "bag" hand and mirror you's "bag" hand are both pointing the same way!
Now stick the bag on your foot. Look, mirror you's bag foot and your bag foot both point the same way!
Now stick the bag on your head. Look, mirror you's bag head is in the dark!
But seriously, everything in the mirror is oriented congruently with this "side" of the glass. The appendages wearing a bag always match up. "Bag hand" and "not bag hand" match just like head and feet do.