By accident I blocked my friend's Xbox Live account, and by doing so I am unable to send her a friend request because Xbox Live says her gamer tag does not exist. I cannot find where I can unblock her to add her as a friend again.
You'll uave to send her a message. That will unblock the account.
Did this solve your problem?
Sorry this didn't help.
Great! Thanks for marking this as the answer.
How satisfied are you with this reply?
Thanks for your feedback, it helps us improve the site.
How satisfied are you with this response?
Thanks for your feedback.