Help with Dog barking!

My little Sheltie goes totally haywire barking high pitch and loud until I leave out the front door ! Then she is fine . Only when people leave , she starts up barking and gets very upset... I have a office room by front door & frosted the glass with stick on . I often say - in your room & she runs in there & I close the door till she calms down & let her out 15 min later. I can now go into the garage to get things and she can’t see me leaving & this seems to help.
But is there any tips to help her learn not to go haywire when I go out the front door ?