Introducing Patience to the horses in a very controlled way is ideal. But you do need to control this.
You are the pack leader and you MUST make it VERY clear to Patience that this is not acceptable.
Your lead and collar are your communication tools along with your voice. This is a very difficult situation for most owners as they are more used to thinking of their pets as furry people rather than domesticated wolves.
It is no good going for an introduction if you do not know that you can control the dog's reaction. More to the point the dog must believe that you are in control.

Before you introduce the animals you should reinforce this belief in Patience. Do not allow her outside unless she is on a lead with a check chain (a prong collar would be best with such a high prey drive (this is a prey response, not territorial)). This is the hard bit - as soon as she starts on the barking you have to give her a correction that she cannot ignore. Use your voice as well, loudly, and keep up hard correction - I mean HARD correction - as you say,"NO, LEAVE IT! NO! LEAVE IT!"
As soon as she takes even a small break to look at you ( don't go all mushy if she tries to get away from you - this is important and if it is not stopped you could end up with hurt horses, hurt dog or worse) you walk quickly backwards dragging her with you and in a very high happy voice say "Good girl, yay! Good girl, good girl." She will then go with you and you must praise her - life is fine and good and you love her but WATCH OUT if you don't listen to the pack leader when she says NO!
Walk back to where she started to bark and if she doesn't bark at this point make her sit and praise her like mad. Go a few steps closer...as soon as she starts to bark you go the full hog again.
Keep doing this until you can get to the fence and she is not barking.

If done strongly enough she will not bark after the first or second correction. If she carries on you should get a prong collar or raise the level of correction even more.
I can just see the heads shaking and the people queing up to tell me I am wrong to treat a dog this way. This dog is showing an ingrained response to a prey animal and needs quick and definite stimuli to tell it that the pack leader does not tolerate that response.

You have to be sure of yourself here - know that you are willing to go through with it before you start - you will have more problems with it than your dog. Ten too soft corrections will make the dog's body sensitivity lessen where one really hard one will teach the lesson, cause less stress and will make both of you feel more secure. Your dog needs direction and in a very strong way to make her understand what she is doing wrong and what is acceptable.