I stopped by Harajuku on a weekend a few years ago and noticed many of the young people in the "Sunday parade" were foreigners. The rockabillies were an older crowd.
A more recent search mentions that Harajuku parade people watching scene has gone
https://www.reddit.com/r/JapanTravel...s_there_a_new/
https://www.reddit.com/r/JapanTravel...e_bridge_on_a/
Since she actually wants to interact with Japanese teenagers, well, the girls were mostly waiting in line for the sweets cafes and some fan/photo book thing I couldn't really understand.
Be sure to make a reservation for the cat cafe ahead of time. Some are too full for walk ins.