The 24 year-old will marry Hefner, who is 60 years her senior, at the Playboy Mansion in June.
A source close to Harris told PopEater.com: 'This is Crystal's special day, and she doesn't want all of Hef's exes there. What woman would?'
One of Hefner's ex-girlfriends, Kendra Wilkinson, recently told how she was upset at not receiving an invite to the event and believes it's Harris' fault.
She told E! Online: 'It's Crystal that does the wedding planning. She's the girl. If she doesn't give me a 'save the date' soon, I'm going to have to put in my save the date with the other wedding.'