Mother-In-Law Invited To Lingerie Shower?

I am hosting a lingerie shower for a friend of mine. Does ettiquette dictate that the future (in this case) mother-in-laws be invited? The grooms` mother and step-mother don`t get along very well and the bride isn`t very comfortable around them yet, not to mention the fact that she will be recieving and displaying things to seduce their son with in front of them. Is it bad manners NOT to invite them?