Really shy girlfriend has helped me in the past,how do I help her?!

I love her more than I love myself really. I don't say it often and I don't show is often either but that doesn't seem to bother her. I can kiss on her all day without her saying anything bad. I can feel on her for a week straight, she'll just keep her smile. But when it comes to us and being physically intimate,that's where the shyness kicks in and my free pass to her body,head to toe,ends when the lights go out or her shirt/short/skirt comes off. She's beautiful so she has no reason to be shy but no matter what I say, she doesn't believe me.

At the start of our relationship I was shy too but some stuff happened and she helped me out of that so I kind of feel like I'm losing on my part because I haven't done the same also. What can I do? What can I try? She deserves to think higher and more of herself and no I don't mean stuck up/snobby,I mean she deserves to think she's sexy,good looking and worthy of every copliment I give her.

She's 21 & I'm 22 so we're adults here,no little kid games or thoughts. Adult things and adult life. I want to ask her to marry me sometime soon,maybe once we finish school.