I replied to the other post you asked this question on but also wanted to add that adding electric to the inside of your existing fencing should pretty much deter her from getting close to it at all.
How many inches do you usually get of snow? Here in SE Ohio we only get up to about 6-12" so I have never had to deal with really big snow drifts. Mine is set about 12-14" off the ground and works well for smaller animals and my horses are very respectful of the electric so they don't even get close to it or try to eat under it.
My reply from the other thread you posted on: I would use something like what I inked below to keep your horses away your existing fence. It will give you a 5" gap between the electric and other fencing, lessening the chance your horse trying to lean or paw the fence. http://www.unionagway.com/Fencing/69...tape-white.jpg