Have you tried asking her to send you an email, and replying it to it? there may be some difference in how you are inputting her screenname (the first part of her email address) and how she has spelt it.
I know in aol you can set a list of email addresses you will accept mail from, but I dont know if anyone not on the list gets a message to say its been rejected.
an example I had was when my mate assured me that his email address was at yahoo.com, but in fact it was at yahoo.co.uk
failing that, she could ask aol online tech chat (which is free, as opposed to a pay service by phone these days)