I understand. She sounds like an absolute darling. Sometimes you just have to let you head take over and tell your heart what to do. You know in your head that you are ready but your heart is unsure. My suggestion is to go for it and get a horse that you like while you have a chance. There are members on here that have been trying to find that "right" horse for months with no luck. Fortunately, since you are looking at boarding her at the current owners place, even if you have an issue, there will be someone knowledgeable around that will be able to help if you can't handle it yourself.
Maybe you need someone to give you a friendly push off the diving board.