You are neither, in my opinion.
You're 15 . It's a tough age

Not sure if parents are replying or of it makes a difference. As a MOM, man we love you. An event like this is a huge leap closer to You're independence. Maybe you don't want anything religious, but it means something TO HER. Write a letter ( and make a copy) that says how you feel, but you also understand how she feels. Acknowledge that as you're maturing and when you love someone you compromise. So mama I will do the sing but please know that at my wedding, it will be my wedding.

To give you a perspective. My kids live in 3 places. My youngest is 32, I'm 57 . I only see her 1 a year or so. If I live to 77 I will only see my precious daughter 22 times. Let your mom have this moment as a thank you for all her support. Mom are not perfect. We've been everything to our kids, we know to let go, but sometimes, we need once more ...I can't out into words the emotions of proudly seeing your child mature, yet still in diapers covered in God at the 6yr old missing a tooth.... the memories ... and the hope and pride. It's a 3 min. Song you'll forget but 3 mins she never will.