Herd bound behavioral problem

Dear Franklin,

I have a 22 year old Arabian named Fawn that has the fire and spirit of a two year old. I like my horses with a little fire, but recently she has developed a problem that is a safety issue. Fawn is somewhat ring sour for the previous owner never rode her outside, but she does well on the trail as long as she has another horse with her. Recently, the pony we have has gone lame and until we find a replacement I have to ride Fawn alone and she FREAKS OUT. I am starting to think, because she was a brood mare most of her life, that she considers the pony her baby because when we had a bigger horse she could easily be ridden away from him.  Fawn is so attached to this pony that when you take her away she is almost uncontrollable.

I went riding a few weeks ago and as I was walking her away from the pony she just started to weave back and forth until finally she stopped, spun me around a circle a couple times and than started back towards the barn. The worst part is that I was pulling back on the reins with all my strength but she would not stop.  

I have been told that I should not bail off a horse if I can help it, but I did not know what else to do for she was so excited that she was coming very close to running into some of the machinery out in the field.  This has made me afraid to gallop her out of fear that she will not stop when told. Don't get me wrong, Fawn is a very good horse and is calm and fearless after some of her energy has been burned off or when she has another horse with her. Is there anything I can do to get her to calm down and pay attention to what I am asking of her? Lounging her works most of the time, but in my opinion that is just a quick fix and I am looking for a more permanent solution. She is a very smart horse and an exceptionally fast learner. I know this can be corrected I just need some advice on 'how?'.

Lynelle