Do i take the chance of proprosing?

I am taking my girlfriend to vegas in June. We will be going for a week. As i have stated in other questions, she does not want to be married for another 5 -6 years and doesn't want to be engaged for another 4. She has given me no reason behind this thought, just that this is what she wants. I have given her no reason to doubt my love. My eyes stay locked on her and never waiver. I have never cheated and make it known that she is my one and only love. I'm an all right looking dude, so could i cheat, maybe, but no propositions have really come up other like twice in 2 years that i have very easily turned down. Anyway, i want to ask her to marry me against her saying she doesnt want to be engaged for another 4 years. But i know she's the one, she's perfect for me and i want her to be my wife and i want to be her husband. Do i take the chance and ask her to marry me when we go away or should i just let it rest for another 4 years?