I recived two friend requests from someone I did not recognize, so I declined them and chose the "I do not know this person outside of Facebook" box. I later realized that I did know the person, and searched for her to add her, but can't find her. She tried to add me again, but Facebook will not let her. How can I undo the blocked friend request? She does not show up my regular list of blocked users.

Taken
When you decline or ignore a Facebook friend request, and then choose "I do not know this person outside of Facebook" you don't actually add them to your blocked users list, so they won't show up there. It just silently declines the request so they don't see you declined them, and then won't let them resend a request. BUT, if you go to their profile and can still send them a friend request as usual. If you don't see them in searches it's probably because of their privacy settings. Ask the person to just email you her Facebook URL so you can paste it into your browser to go to her page and send her a friend request.
Let us know if it worked for sure, it should!