We have a two year old Missouri Fox trotter, we are going to use her for field trials.  She seems to charge our dogs when they get in the pasture.  She recently pinned down our female weimaraner and pummeled her with all four hooves.  Does anyone know how to train her to stop this and get her used to the dogs?

how is she under saddle?

My horses do not like dogs in there pasture as they feel threatened but under saddle they are fine.

My first dog horse was like that, and this is how I brought him along -

Is she OK with the dogs while under saddle? If not, have someone bring a horse-wise dog near on a lead, and get after the mare when she makes the slightest move - pins her ears or whatever. Then gradually as her behavior improves have the dogs closer for longer times. As the mare learns to be nice, give her praise and treats.

Then try the same thing with her saddled but you dismounted,  holding her reins or lead.

Then have a dog brought near while the horse is on halter and lead.

You see how it goes - gradually work your way out of the picture.

Important when you start that the dog is respectful of the horse - you don't want to start out with a wild and crazy puppy.

If the horse bothers the dog in the pasture because the dog is deviling her, then get after the dog. My horses have learned to tolerate the dogs running and sniffing some, but I prefer they don't take too much grief from the dogs because I'd want them to be nasty to strays.