I need some help with my horse !!!?

I would watch the fly bite for a little longer but if it is not improving call the vet out. It would help to know what she is doing when you try to bridle her. If her teeth have been floated, and her mouth inspected, my only guess to your problem is that she has learned she can get away with it. She knows if she does that she won't have to wear a bit so she is continuing to do it. You may need to correct her and possibly force her to take the bit. Use your thumb on her top gum to open her mouth and put the bit in being careful not to hit her front teeth. If the bit is cold simply hold it between your hands to warm it up, sometimes a little hot breathe helps too.