church wedding officiate

so i grew up in a christian household. said my nightly prayers had the reverend over all of that crap right? well my mother and grandmother are heavily religious. i’ve stated that i’m not and they said “don’t worry once you get older you’ll realize god is inside of you and that you’ll need him in time of need” okay sure. so i’m with my current girlfriend and we started planning our wedding for fun. she’s atheist i’m agnostic and most of her family (her mothers and most of her siblings) are atheist as well. my mother has this idea that i have someone from the church officiate our wedding. this makes me and my girlfriend highly uncomfortable. she even said “i respect your mother, but no.” and im the same way. my mother wanted me to first get married in the church (i’ve left the church for about 3-4 years now. my grandmother and mother are still active members and my father volunteers once in a while. he’s agnostic.) but now she wants someone from the church to officiate the wedding. how do i tell her no without breaking her heart?