It's taken me a long time to realize/accept this, but some people are simply mediocre/average. We're not all equal and some are just better than others.
In fact, I think MORE people are average than they are above average, but we focus so much on those that appear to live the type of life we want that we *think* that's the way the entire world is.
It's not.
Obviously, there are things she can do that you can't, but you need to realize that you have skills she doesn't. You just have to find those and HOLD ONTO THEM. Find the part about you that makes you surpass not just her, but everyone. There's nothing wrong with trying to find your "thing" and if you don't think you have one GET one.
Take up a sport. Write a book. It'll take effort, a lot of effort, but if you're not lucky enough to be born with gifts, looks, skills, etc. then you have to put in the effort or live out the rest of your days in the Land Of Averages.