Mail Sending Unauthorised iCal alerts to a coworker's e-mail

Hi Everyone,

I am having problems with Apple Mail sending notifications of events from iCal to another coworker of mine. This is very strange, and I can't seem to find any way to remedy it. She used to use the Mac that I use for work, but it has since been formatted and everything erased.

If I go to my sent mail folder there are e-mails that I didn't personally send, that look like this :

Title: Alert Sam/Serge Pictures

Body: 8 July, 2014 3:30 PM : Sam/Serge Pictures

Does anyone know where I can reach these settings and turn them off somehow?

Thanks!!