I'm pretty sure this is something to do with her local system. I can log in with her credentials perfectly well. She's tried three browsers (chrome, firefox and safari). She's cleared her caches, cookies on each of the browsers, rebooted. I had her clear her DNS cache in her OS. She's on a mac running Yosemite.
The only other time I have seen this is once after I created a test site and was moving between the live and test site. I was able to clear it up by rebooting and clearing the browser cache and deleting the cookies.
thanks in advance for any suggestions.