Wedding Invitation Ettiquette

A very close friend of mine is getting married, we also work together. She is only planning on inviting me and her immediate manager to her wedding..Mainly because it is a small wedding, and she really doesn`t want to invite alot of people (from work) that she isn`t really close to...The problem is, several of our co-workers have assumed they are invited...and they are not. How does she tactfully explain they aren`t invited....???