You always want to be safe! So if you start going in the stall, just go in and stand along the wall and read a magazine or book. Don't look at her, talk to her or acknowledge her in anyway. Then as quietly as you entered the stall, leave.
Stand in different parts of the stall when you do this. Again, being safe and watching her. If she is getting really upset, go outside of the stall and work on that until she's not upset and you can move inside.
Eventually, she'll start coming over to you. Even if it's within inches... it's progress! A horse like that needs a lot of patience and time. Don't rush her and you'll have a great chance. Good luck!
Unless it weighs a ton... it's just a horse. Draft horse motto.