Hello, I understand that you have a question about your bunny's ability to see and how good her depth perception is and I'd like to help. I'm glad to see you are thinking ahead to keep her safe.
Rabbits are a prey species and as such have evolved to be able to see with a very wide range of vision. Their eyes are placed on the side of their head such that they can see almost directly behind them and very well on the sides and above them. In fact the area they have the most trouble seeing is directly in front of them. There is a small blind spot there. With this wide angle ability they have sacrificed good depth perception as there is only a small area that both eyes can see in front of them (which is how depth perception is gained), and part of that area encompasses their blind spot. You will notice your bunny moving her head around, in a bobbing motion or sometimes to the side to see things directly in front of her.
Because she is a prey species she will also startle easily.
I am afraid if she is startled, with her poor depth perception and a blind spot in front, she would accidently jump off the porch between the slats. I wouldn't let her out there if there are open areas big enough for her to fit through.
Perhaps there is a way to fence off a small area just outside the door so should she get out, she doesn't have direct access to the slatted areas.
Best of luck with your girl, let me know if you have any further questions.