Meeting Invite arrives from Wrong ("send-as") Sender

Outlook version
Outlook 2010 32 bit
Email Account
Exchange Server
We are running Exchange 2010 with Outlook 2013. The Executive secretary has been assigned Full Access and Send-as permissions to the Executive Director's and the Associate ED mailboxes on the Exchange backend. When she attempts to send a meeting invite from the ED, recipients receive the invite indicating it was sent from the Associate ED.

In checking the mailboxes, the only thing I found was that she had also been assigned as a Delegate on the AED mailbox. This, by default, assigned the "Send-on-behalf" permission. I know having the Send-as and Send-on-Behalf permissions assigned at the same time usually causes some sort of conflict, but I don't know if it may be causing the "wrong sender" issue. Was hoping someone else had run (and fixed) the same situation.