Practice trail riding in the arena with other horses first. One thing I do sometimes is we play follow the leader, and every person gets a chance to be leader. You would walk and follow, then the first person would say when they wanted ot be done and go to the back.
Mae sure to groundwork her a lot before getting on, practice a ton in the arena, and when she is a little bit better in the arena, then walk around the driveway until she gets good. One thing that might help is when she starts acting up, stop and back her up. She doesn't want to be left behind obviously right? SO when she acts up, make her go farther and farther back. When you trust her not to throw a fit, then catch up with the horses and stop. It's ok if people are behind you when you do this - just make sure they know your situation with the horse so they will give you space.
🔫 Don't Tread On Me 🐍