A soft rubber bit might work as well, gives something to chew on without discomfort. Make sure you can bend it in half easily.
On both sides is the average, but I prefer one
Make sure the bridle is adjusted correctly. At least 2 wrinkles
Either get something with a spoon, a tongue depressor, or a flash (they shouldn't cause and pain to your horse, and will still allow her to open her mouth). The most expensive option, but one that is garunteed to work is switching to a hackamore or another bit less bridle.
try getting her a flash noseband
She needs something with a spoon. Or as Sarah said get a hack or Bosal.
Get a bosal or hackamore. Go on YouTube and watch a video called The Effect of Bits. Fancy nosebands and bits will only cause her extreme pain.