Rachel, I'm not surprised you are confused! Running is one of the simplest forms of motion, and the only rule to the game is not to start your race before the gun. There are no rules for training. It seems that this is your first half marathon, which is a popular distance. I remember that prior to my very first one I didn't want to have gone further than 13.1 because that would deflate part of the challenge (for my sponsors). Conversely I wanted to be confident that I had done enough training. Personally, I took it as far as 12 miles on a few occassions in the preceding weeks.
Subsequently I was running half marathons as part of the training build up for marathon races, so was building a far greater endurance base (to 22 miles).
Do what feels right for you. If you can do 12 now, I'd keep that going until the week prior then taper off the distances. You'll hit the line as fresh as a daisy.
(One other piece of contradictory advice you'll come across is about pre-loading with pasta the night before. This may be fine, but I'd warn against pigging out and being fat and bloaty on race day)