Do not go out at all if your girl panics when you are trying to lead another horse off her. It is good however that you know this, as she has done it before, so you can work on it.
The horse you are riding should be the sane one, I have had many situation ponying were I am thankfull my boy behaved so darn well, also had some hairy moments with both horses being silly
but I was able to keep them in control.
One of the main things is that YOU have to have enough knowlege on ways to control your mare if she does play up, as even a bombproof horse will have its moments. If you are confident in your ability to do that, only then would I be thinking about trying ponying another horse.
The horse you are riding should also be able to be controled with you using only one hand ( with in reason ), and you should be able to ride with one hand comfortably on her .Also the horse being lead should actually know how to be lead, you don't want trouble to come up and the lead horse to not respond to you.
On that thought....yes start in a enclosed area...correl as you call them.
I would advise that you introduce your mare to the horse you wish to pony off her before you do anything else, make sure she is comfortable with them being all around her , as when ponying both horses are walking reletivly close together. If she's %100 accepting of that horse being around her then...... Just sit on her , holding the other horse, pats and praise for calmness. Take a small walk , then stop and just slowly progress to longer walks if they are going ok. If either horse seems worried by the whole thing just stay at a stand for a bit longer to get them calm again then walk on slowly again.
You could also have one person on the horse being lead , so if something does happen you can drop the lead to control your horse, while the other person takes care of the other.
Just take it slow. Keep the horse being lead's head at your knee, and don't forget to praise both horses for there efforts.
Ha...sorry for the long post :roll: hope it helps some....