OhioDad,
I do have one dd who has skipped a grade despite being one the youngest in her grade as well. Being younger isn't always a reason to rule it out. However, it is a very, very good idea to have a complete IQ score in the 98th percentile or above and to have the child be working multiple grade levels above her current grade in all academic subjects if you are going to consider a full grade skip. Another option would be seeing if she can be accelerated in math only -- commonly referred to as "subject acceleration."
We've never prepped our girls for Explore or SAT tests either. My understanding from talent search is that they don't encourage a lot of prep work although I know that some people do so.
Have you gotten her Explore results back yet? You may be able to use those to advocate for more challenge in math if she did as well as she thinks.
When your dd is a bit older, you may want to look into Math Path summer camps:
http://www.mathpath.org/ They are held on a different college campus each year so they might have one close to you in a few years.
