CBF mentioned that she knew Garrett through her brother because they were friends.
If Chrissy was spending every day during the summer at the country club pool (presumably without her parents), a likely way that she got there was through one of her older brothers.
If she really did go to parties directly from the country club, it is reasonable to think that she was tagging along with her brother.
I don’t know many parents that would let their 15 year old daughter spend the day away from home, without at least understanding her transportation arrangements.
I have two older sisters. The only ways that I would ever have been allowed to spend the day away from home during the summer were if I was with a friend’s parent, or with one of my older siblings who could drive.
Apparently, I didn’t lead such a sheltered life as I thought I had. I was able to ride my bike all over town by myself or with my bestie who lived down the block. All was fine as long as my chores (everything was on me) were done and I was home to cook dinner.
Junior year, my bf could come over without parents being there but it was all innocent. I was very straight laced.