AD & Exchange 2008 server - changed AD username, but Exchange still shows old username, and cannot add her to "Send on behalf of" mailbox?

We have Win Server 2008 AD and Exchange 2010 server. I changed a username to a married name -

* old = FnameSalguero

* New = FnameGorden

She can login, access everything, etc. However I am trying to add her to a group mailbox to Send on Behalf and when I search for her, it shows her *old* account name. Everywhere else in the system it shows her new username.

https://i.imgur.com/QPkwyZS.png

I've been searching for days and can't find a solution.. Thoughts?