I hadn’t done the upgrade to 2.6.2 yet on the blogs (she hadn’t been online, so I didn’t know it needed an upgrade) – but once I did that, I was able to log in.
I did notice that both of the blogs I cannot log into (both for the same friend) — when I looked in mysql, they both had a new user with the name WordPress, but no email, etc, and the registration date was 0000-00-00. Not sure if that has anything to do with it, but I’m definitely deleting that one out.