I think it depends why you are rethinking it. Did she do something? Are you just drifting apart? Did u ask her for the wrong reason?Whatever your relationship with her is expect it to be worse after you demote her from your wedding. It's a touchy subject and although it's not a big deal to be in a wedding it can really seem like it to some people. I would have to know more to give good advice but just be sure you think about her feelings and your future relationship.