Hey Jennifer,
If they used the Send Marketo Email button, that means they used an email that you have in Sales Insight. You can create trigger campaigns (Trigger: Is Sent Sales Email) to look for when Sales Insight emails are sent and add them to lists, create completed activities in SFDC (which is what we do), created Interesting Moments, etc. The email should also show in the Email tab of Sales Insight, with whether they opened and/or clicked a link.
Just depends on where you want the data to show!