She's not going to be able to sign in as long as she remains in the moderation queue. You need to approve her registration first. There are 21 people in your moderation queue that are all in the same boat. They have requested to register but have not been approved.
Why do some people remain in the moderation queue? Is there something that is checked off when they are invited to the forum? Most of the time they are invited and then they are automatically put in they requested group.
It seems this person tried to register before an invite was sent. I don't see that email address on an invitation list and registration is generally available, but moderated. Registration is not set to invite only. In that case, anyone that registers without an invite, or before being invited, will be in the moderation queue. Your settings indicate that anyone invited will bypass moderation, but will not bypass if they register without or before an invite.
When you block a person, they can no longer invite you to a private message or post to your profile wall. Replies and comments they make will be collapsed/hidden by default. Finally, you'll never receive email notifications about content they create or likes they designate for your content.
Note: if you proceed, you will no longer be following .