Sounds like you're doing a great job with her! Bless you for taking her; I'm certain she will be a blessing for you too! One thing that will help her trust you and any other handlers working with her is by handling her face A LOT with gentle scratches and rubs. I'm curious to see if you have worked more with her under saddle since Jan.
If you haven't watched any footage from the Road to the Horse, available at Clinton Anderson and I think Chris Cox (both champions of this competition) I highly recommend them. Obviously you have more time than what they had, so just break the different exercises down to baby steps, and do them more repeatedly. I also recommend the Riding with Confidence series and Gaining Respect & Control on the Ground by Clinton Anderson. These and bunches more can be rented at www.yourhorsematters.com for a very reasonable fee.
Another poster said to not be sneaky around her, I agree; this will only make her more suspicious of you. After you have introduced another "new" item to her and she calms down, make sure to do something she likes. Just a release may not be quite enough for her becuse of her being so mistrustful. Glad to see that you are also making sure to put her in her place if she gets a little pi$$y, too. Finding the balance between desensitizing and gaining a horse's respect is a fine line, and it's different for every one of them. Congratulations! We need more peeps like you who take their time and give these poor creatures a 2nd chance. Hard to do in today's economy!