Good for you! You can have lots of fun with poles and cones, setting them up in a weave pattern, and making a bit of an obstacle course. You can also create lots of obstacles with a bit of wood and some imagination. Given that you describe your mare as green broke, this would be a really good way to desensitize her!
This course would be easy to build, and looks like a lot of fun! Start by leading her from the ground before you ride her over all of these, and maybe just do one per training session, before you put them all together. This is a great way to build communication between horse and rider.