Not sure what a college admissions essay is supposed to look like so I can't give you specific advice, but I can give some honest feedback and constructive criticism (beyond simply saying "spell check! if you turn in a 'collage essay', it will not be read." )
To be blunt it was boring, and had no setting whatsoever. After a sentence or so I lost interest and it could have been two people discussing snowboarding, or two people at the pharmacy trying to decide on which hemorrhoid cream soothed the fastest. I'm not a snowboarder, so it isn't that interesting to me. (Although I'm sure if I were I probably wouldn't stop nodding "mm hmm. Yup. I remember those days..") If I wanted to listen to people talking about topics I don't understand and they don't appear to want to keep my interest, I'd watch CNN. lol
Caveat: I'm no writer! But I was thinking something like...
We had arrived at the slopes early, my sister and I both buzzing with anticipation. As the sun crawled across the cloudless sky, however, her mood changed to frustration.
"I can't do it!" she blurted.
“Its easy once you get used to moving sideways," I encouraged, "you can’t keep the board flat on the ground. You have to ride on the edge just enough to prevent the board from wobbling. Let’s go back up the hill and try again.”
Chelsea followed me back to the tow rope pouting all the way to the top.
[... insert the filler about lessons on the bunny slope, but cutting back on the dialog and adding descriptive words to paint a picture (try to make the reader BELIEVE they are there watching her 'get it')...]
Finally conceding to her desire to leave the practice field and try one of the trails I led the way to the lift. Slowly we ascended as the hard wooden seat softly jerked and swayed from the pulleys that operated it as well as the countless skiers getting on and off. At one point high above the ground below she appeared to be sliding forward. "Are you alright?" I inquired, "you're slipping!" "It's the weight of the board, pulling me down." "Place the ski across your unstrapped foot to support the weight." Chelsea adjusted her feet and the rest of the trip to the top went by uneventfully as the top grew ever closer.
[... insert the filler discussing advice at the top, keeping in mind to keep the reader interested and believing s/he is at the top with you, watching....]
Chelsea started off on the left most trail as I cheered her on, but had barely skied one hundred feet before three teenagers on skies appeared seemingly out of nowhere. They coated her with kicked up snow like frosting on a cake as they passed close enough to cause the fabric of her snow suit to flutter.
Racing to her side I pulled Chelsea to her feet and helped brush off the snow.
“Whoa, that was close! I felt the air rush by,” she exclaimed.
“Yea, those skiers need to be more careful. There is no way they didn’t see you. You aren’t hurt are you?”
“No, I’m fine.”
“Ok, is snowboarding fun yet?”
“Yea, when I get going its fun," she beamed proudly. Chelsea broke into a large smile. "Falling is too. It doesn’t hurt like when falling on skis.”
Can you see the change from the beginning of the essay to the end? That 'light bulb moment' at the end where she discovers, finally after her struggle against the environment (in this case maybe struggling to be able to stay upright and turn in the snow) and also against her self (maybe an inner struggle against that voice that says "give up! it's not worth it!"), she is triumphant. Another thing I tried to do was foreshadow the run-in with the teens by mentioning the other skiers on the slopes. When was the last time you went snowboarding and had the slopes to yourself?
...anyway... my $0.02. Best of luck!