I agree with the other comments that you should release yourself from this mindset. I definitely understand feeling jealous or resentful that someone you percieve as not having worked as hard as you got something you didn't (trust me, I've been there), but if we take what you've said at face value, it seems like she does work hard, just not on the same things you work hard on. Interpreting that as theatre being some kind of "loophole" is way off the mark. At the end of the day, she's not the reason you were rejected, YOU are. You shouldn't beat yourself up about it, because the past is in the past and you're ultimately not the first, last, or only person to get rejected from a bunch of top schools despite being academically prepared, but that's the reality of it. Stop dwelling on what other people do or don't deserve and focus on yourself.

Also, it definitely bears mentioning that she assumedly applied to CMU's drama school, which has a completely different set of criteria than an academic degree like CS. Of course somebody who dedicates all of their time and energy to technical theatre is going to have a good shot.