Trying to use Special:UserRights, friend's account exists but getting error that says it doesn't

[hallow summit]

There is no user by the name "<username>". Check your spelling.
That's the error I'm getting. Don't want to say their username, my username, or my wiki name publicly for privacy reasons.
Their account was made through the cvt team because their ip was blocked, and I suspect that might be why. They've already emailed asking for their account to be attached to my wiki, just wondering if something can be done on my end earlier or something

[abstract crater]

If they can't attach to your wiki by logging in there, then there's not much you can do but wait for someone to attach it.