I don't want to conduct my mothers marriage ceremony
Is there a reason why you don't want to conduct it?
It's a pity to see my mother marry a man who doesn't deserve her.
If you aren't comfortable with the situation you don't need to conduct it. Just because they are your parent doesn't mean you owe them anything.
I'm going to obey the rules of my etiquette and be respectful. I'm still going to conduct the wedding even if I don't like it because it's wrong for me to disobey social norms.
You are a good daughter. You should do what you feel is best for you.