How would you break the news to your mom or would you?

We have decided to name our daughter Blakely Raine. I got to pick the first name and my boyfriend picked the middle. His mothers name is Lorraine and he wanted to name the baby after his mom. I couldnt find anything from my mothers name that would go with Raine and I really wanted us to use something that wasnt named after anyone so nobodys feelings would be hurt. Hes already told his mother that the baby will be named after her. I know this is going to hurt my moms feelings when I tell her. Should I tell her and if so how? I asked him to tell his mother not to say a whole lot about it at the shower b/c my mom will be there and I know its going to hurt her.