college acceptance letter.

Assuming the college is somewhat professional, they'll probably look for people that differ from the rest she should share what personal interest she has in Psychology. Be personal, but she shouldn't exceed the personal aspect of it too greatly, or else it looks like you're writing your grandma a letter on how your doing and what you want to do in life. Be precise and never use two words when one can mean the same as both of them. What will make HER a better student than the rest for that major? Can she fulfill the challenge? Can she excel in every aspect of the courses she must take?

Answer all those for them, but like your professor said (one of the only things he really made sense on), don't be arrogant about it.