If you look in Messages, in your "Outbox," you've probably already sent her several copies of the message. It give you the error AFTER it sends the message. You might want to delete the additional copies of the message that you might have sent her.
If you don't see any messages from you to Priestess Skye, go to "Compose," and type "Priestess Skye" in the box at the top of the message area and you can send a message that way as well. If you're still having problems, please let me know!!
~~Wiccan~~
PS - I replied to your message, cuz I found that in my inbox before I responded to this!!