She does sound wonderful, but just because she's a good horse doesn't make her worthy of breeding. We must take into account a lot of things before breeding a horse. Good bloodlines? Almost perfect conformation? (An if not, is the stallion strong in the areas where she is weak?) Personality? You say that she has a good show record, so I won't ask again.
Do you think you're qualified to raise and train a foal? I know nothing about you or your skills, so this is up to you. Remember to be honest with yourself.
I am a little concerned when you said you couldn't stand to loose her... Breeding is dangerous, especially for a maiden mare that old. Something could go wrong, and if you feel you couldn't live without, you shouldn't breed her.
Sorry for being so uptight. It's just a big decision and requires a lot of thought, honestly, and planning.