Most Helpful Girl
No, just make it clear you don't want to be married right now. If she is persistent beyond your patience, then let her know your getting to the point of ending the relationship if she continues. Then if she continues about it, break up. Don't just break up right away, at least talk about it. That's what relationships are about.
Most Helpful Guy
I think you should first talk about the reasons you each feel the way you do and make sure you both understand each other, then try to reach a mutually agreeable conclusion. If you're just not ready, but think some day you might be, see if she's willing to wait a year and then think about it again.
If you can't agree, and she insists on getting married soon and you don't want to, then you'll have to think about what to do. That kind of disagreement seems like it could cause a lot of damage to the relationship because she could be feeling hurt that you don't want to make that commitment to her and you could be feeling pressured to do something you're not comfortable with and neither of those seem like they can be good for the relationship.