We just learned this in our intermediate class at petsmart. It is called the wait command (different from stay).
Start out not doing it at the door--just in the room. Put her on her leash. Have her sit, then move your finger to one side and say wait. Drop the leash. Back away a few steps and do the finger and "wait" again. After you back up a few more steps, then tell her "okay, come". Do that over and over, lengthening the time before you allow her to come. Then practice it at the door, saying "wait" again as you start to guardedly open the door. Then praise and treat.
Of course, it takes lots of practice. good luck
