Sounds like she might be testing you. You need to ride her into the bit with your legs. Think legs and seat as main aids, hands secondary. Ride her into the bridle, don't pull her head down where you want it, but "ride" it there if that makes any sense? As far as the lead get her comfortable on that lead before you even ride her. Work her in the round pen or on the lounge then in side reins until she is truly comfortable with that problem lead. Then when you ride her, make sure you are asking correctly. For a correct lead, ask with outside leg, inside rein and inside leg at the girth. Push their hindquarters over slightly to the inside, this will help them push off.