Don't think about it Derby. Just move on and if she finds her way back into your life than that's great. Don't pursue, let her come to you is my advice. If she doesn't than others will fill in the void she leaves behind.
You don't have to send an email saying it's over, just let it be.
I know it's easy for others to say...I have been blessed (or cursed) with an on/off switch for most of the people that come into my life. It seems much easier for me to disconnect from people than form connections with them. I may have oversimplified my first comment