I agree with JDI, this horse is nowhere near ready to be in any form of leverage bit. The horse should be soft, responsive, supple, and have a very good idea of at least the basics of neck reining all in the snaffle long before you even consider moving to anything else, especially a leverage bit.
While I do believe that a western ridden horse can be ready for a curb bit in a relatively short amount of time, the rider/trainer has to really know what they are doing in order to do it properly without ruining the horse's mouth or their mind.
Has this horse ever been to a trainer of any sort or did you just sort of start riding her 6 months ago? How much training experience do you have? Have you ever worked under a trainer to learn the proper way to start a horse under saddle?
Just my guess, but I would be willing to bet that this horse was never taught how to properly respond in the first place. While there are some horses that are just hard from day 1, the majority of "hard" or "insensitive" horses were made that way by improper handling during their first experiences with training.
You need to go back to the snaffle and either find an instructor or a trainer to help you. The most crucial part of training a horse is the timing of the release of pressure. If you release pressure at the wrong time or expect too much right from the start, then you'll end up with a bracy horse that is unwilling to respond the way that they should.
You need to go back to the very basics of suppling and teaching the horse to give to the bit. Because she's been allowed to be so unresponsive for so long, you're looking at a lot of work and a lot of time to get her fixed. For that reason, I suggest you seek help from someone more experienced in training horses. Someone who will know when to be steady and when to get a bit more assertive with her.