I'm trying to evaluate the usefulness of Google Adwords for a friend's site. I'm trying to count the number of sales per month, and see how many have found her page because of the Adwords campaign. Her site has an online order system, but she also gets customers that buy just via the email contact and never use the online order system.

There aren't many conversions per month (usually only one to three), so I don't want to miss any conversions when I want to gauge the effectiveness of a campaign. Is there a good way to also include those conversions?