Horse breaking into canter when riding in rear

I am a new member here and wondered if you could help me. I have been riding for about 2 years and have owned my horse for about six months. I have had a recurring problem when trail riding with others and we are not the lead horse. If we are leading she will canter relaxed and in control. If we are in the rear, then she will frantically surge ahead. This is particularly a problem if the horse leading spooks and unexpectidly breaks into a canter, because my horse follows suit and charges forward to catch up. I do have a trainer and we will be taking our lessons out on the trail to address this but I wanted to get some suggestions in the meantime.

I need to address both issues. One is teaching her how to not bolt into a canter when I ask for it on the trail when she isnt the lead horse. Second is teaching her not to bolt into a canter on her own when the lead horse spooks and breaks into one himself, which doesnt obviously happen often, but has happened. This is the one that is really scary!

My friend and I plan on taking them out and start off by doing lots of walk, trot transitions with me in the rear and if she gets excited then doing a one reign stop and circles until she is relaxed and also playing leap frog at the walk, trot. I plan on doing this for at least a month before moving up to trot, canter transitions because it freaks me out thinking about doing it sooner and I want to take my time to really teach her. I will also go out with my trainer, as I said.

Am I approaching this correctly? Any other suggestions? Will this help with my second issue? Thank you!!

Am I

What I do with all my horses is practice standing them in a field and have another rider first trot, then canter away from them. Once the horse can stand calmly while the other horse canters away, I have them pick up the trot and follow. Once they are calm at trotting, I have them canter. If the canter gets out of hand I make them stop, then walk calmly up to the other horse. My horses hardly ever get to ride in front or pass another horse while trottingor cantering on the trail. Its also very important that you always cue your horse to trot or canter after another horse, as opposed to just letting them follow.