How to find the email a threat is coming from?

Product: Anti-Virus for Mac Home Edition

An friend of mine has been getting a couple of threat notifications from Sophos Anti-Virus with the text "Virus/Spyware Troj-Redir-T has been detected and listed in Quarantine Manager". Obviously somebody is sending her this virus again and again. The threat seems to be in an attachment by the name FullDetails.html but she has no idea with which emails these attachments are being sent to her. She has no emails with such an attachment - possibly because Anti-Virus removed the attachment from such emails.

Is there a possibility to find out the exact email that contains the threat?

If not - why not? Are there possibly other products (whether from Sophos or a different company) that would be more specific about such a threat?

Thanks for your help.