I think side reins are great for lunging, I use them all the time, as long as they are not trapping the horses head into a uncomfortable position, mabye just slowly tighten them over a period of time. I would also recomend long lining, I LOVE it and I taught myself by reading books and asking other people at the barn, as long as your horse doesnt freak or anything when you make mistakes and wil be ok with you trying it out on her (haha, my horse was so patiant the first day I tryed long lining!) then I think you and your horse will find it very helpful. :)
If there are no horses in heaven... im not going.