Join Date: Oct 2009
Location: Just south of sanity
The first thing is to find out if the mare's parents were registered.
If they were, you'll need their registration names (and possibly numbers) as well as the name of the association where they were registered.
Once you have all that, you can contact the registry and see what they require in order to get your mare registered.
At 8 y/o, even if you can get all the DNA information and paperwork together, it's going to be fairly expensive to register her. That is, if they don't have a cut off registration age. Some associations do.