She was the only teenager at the time. Like her younger sisters, Kelsey was well behaved.
In addition, one of her sisters mentioned that whenever her parents go out for any amount of time she will have to baby sit. Kesley states that it's evident since at one point when her mom went on vacation in Hawaii she was left to watch over her siblings over night when her father went to work and she came back from school.
She also stated to Jo that she's a straight A student, and has never broken her parent's trust, yet she's not allowed to hang out with her friends when it's only 3 or 4 in the afternoon.
When Jo arrived she was only 13 years old. As of 2016 she is 19 years old.