Join Date: Dec 2011
Location: North central Iowa
What country are you in? In the US, we have a bit of a different scale. I haven't evented but am looking into doing it with my QH. I also agree that your mare is long-backed and downhill, but I think she would be safe at the lower levels, which is what you'd be doing for a few years at the least unless you are one of those extraordinary people that move up really fast.
In the US, these are the levels:
Intro/Green as Grass/Pre-Beginner Novice/Starter - This is 2'3" I do believe and may not even have water. You do the Intro dressage test.
Beginner Novice - This is the first recognized event by the USEA if I am correct. Fences are 2'7" with 3' brush. You also get to experience water and a ditch on some courses.
Novice - Fences are 2' 11".
Training - Fences are 3'3".
Preliminary - I feel like this is the gateway to big time eventing. Fences are 3'7".
Intermediate - 3'9".
Advanced - 3'11".
And then you've got the FEI system, which is where you see the CCI*, CCI**, CCI***, and CCI****. The Kentucky Rolex is a four-star event.
In the least, I think you should give eventing a go. It will keep your mare entertained, you entertained, and both of you in great shape. If you decide you do not like it, all three phases that you've worked on will come to help you out in other disciplines, particularly the dressage, and that's even if you decide to keep going western.