how long u know her?
i told ya, it's BEST don't seek approval like this, find out how strong her attraction towards you (ie does she find u often, touch u often, get close to you etc)

if you got rejected, hailat i tell u friendship dies

I would say Diane, we have known each other for about say 1-years and during this time,  I really enjoyed my time with you.

I have come to know you as an intelligent, kind and funny person and I really like you and would like to be more than what we currently are and would like to know if you also feel the same way that I do.

This way gives you more room to safe face if Diane does not feel the same way. 

But that's just my opinion

PS - you can add beautiful to  intelligent, kind or funny but some women want to be appreciated for their inner qualities and some outside.