Middle name dilemma.. help!!!

Okay so, my husband & I decided if we have a boy down the road, he will be named after my dad. We love my dads name. So to honor my husbands side of the family we would use his mom's name as our little girl whose due in 5 weeks middle name. But I feel like my mom will be super offended. But I think fair is fair. A name from each side of the family. How would you go about telling your mom this??