I checked her deleted items and they weren't there + I also explored the "Recover Deleted Items" option in Outlook. There were 100s of deleted emails in there but she said that those were definitely ones that she wanted to delete. No sign of the missing ones from her inbox.
She has been through every folder in her outlook but there is no sign of them. Exchange hasn't reported any errors, either on the client machine or the server. Also, the only folder that seems to be affected is the Inbox, every other folder is fine.
Does anyone have any idea what could have happened?