hmmm she DID use dashes to separate her first, middle and last name. Could that be the issue?? If so, is there a way for me to correct that for her or do I need to delete her account and have her re-register with no dashes?

Dashes as "-"? The "-" character is invalid in usernames. If she managed to register an account with "-" in her username this is even a bug in Elgg as it should have stopped her from doing so.

Has she already posted content? If not I would suggest to remove the account and ask her to register again or you could register a new account for her and send her the login password. This is most likely much easier than fixing the problem in the database.

cool! Thanks for the fast responses!

She's not been able to post any content. As soon as she registered and tried to go to her profile it gave her the error message. I've deleted her and I'm getting her a new account set up without any odd characters ;) 

Are display name and username the same. The username would have to be used to log in (just in case...).

Is the account activated. Only the first admin accounts get activated automatically. Any further accounts need to be verified either by email validation or by activating the account in the admin section.

Are there any special characters included in the username? While it should have impossible to register the account then already there might have gone something wrong that did not stop the account to be created but is now resulting in the login not being possible.

Are you trying to login on the same computer you are able to login yourself? For the login to work it's necessary that cookies can be saved. But if it works with other accounts on the same machine this should not be the reason for a failed login.

if there is a problem with the username as iionly suggests, you can try using the email address as the identifier

thanks guys! we got her fixed up. I think she was trying to use the display name :)