Sorry for my bad english but I realy need help. I just can't understand what is the problem.

I have a code:

Function Riverwood()aRiverWoodShip.Enable()PettyInRiwerWood.ForceRefTo(fPetty)fPetty.MoveTo(cPettyTeleportRiverwoodMarker)Game.FastTravel(bTeleportRiverwoodMarker)

Everything work just fine. I need to enable some object and teleport Me and NPC Petty on that object. It works great, just how I imagine it. But sometimes, when I teleport from Whiterun (for example), NPC Petty just do not appear. Sometimes she is appears, sometimes not!

I tried to move to my NPC in game, and I found that she is stock in WhiterunWord outside the city, but not in Tamriel.
I just don't understand why sometimes it works and sometimes not Can you help me please? Thank you for any response.