If you face and focus (actually look) on the flank of the horse, this will promote movement. Horses move away from pressure/obstacles..... Same goes for asking them to stop or slow down. If you take a large step towards her nose..basically suggesting that your are getting in front of her...(even though you are not close) and hold your hand up and say "whoa" or "ho" or what ever your stop word is, while gently pulling her head towards you... she might instinctively stop for you.