"Bitting up" refers to the idea of putting a horse in a harsher bit for a few rides to get their respect back and get them listening to the bit again. I am not a huge fan of people doing this unless they really
know what they are doing. There is a fine line between doing it right and lightening them up and doing it wrong and making them worse.
Wild_Spot hit the nail on the head, if the horse is not responding to your cues to slow and rate, then pulling harder with both reins certainly isn't going to help. Completely ditch the idea of stopping or slowing down by using both reins for a while. Start at the walk and ask for the stop with your seat and legs. If she doesn't stop, then take one rein and use a one-rein stop. Then do it again...and again...and again, switching up which rein you take to stop her. She'll soon start listening to your seat and legs and when she's solid with that, you can move up to the trot. Then, when she's solid at the trot, you can move up to the lope. When she's solid at all 3 gaits like that, then you can begin to re-introduce the two-rein stop at the beginning, with the walk. Of course, you can only do this effectively in a standard snaffle.
Clinton Anderson has an excellent video about this that I saw on TV. I can't find the video but here is a good article about it. Clinton Anderson: Using the One-Rein Stop for Western Lope Control Slideshow
There isn't going to be a quick fix and you probably won't see improvement in just a couple of sessions. It will take lots of time, patience, and repetition.
Edited to add: Breaking at the poll often isn't something that will come in one ride. On a horse that is already bracing, you have to be that much more perfect about releasing pressure at the exact right moment. If you get her soft every other way, then breaking at the poll will come in time with proper handling.