Every historical character has their own theme that girls today can learn from, and Isabel and Nicki are no different! These are the "lessons" American Girl posted that are in their story:
Express your girl power: "Although Isabel and Nicki have their differences, they agree that girl power is important—they just express it differently! For Isabel, girl power is about the messages of the Spice Girls, expressing herself loudly, and standing up for herself. For Nicki, girl power is about learning to use her voice, not being afraid to mess up, and the alternative music she loves. Both twins have girl power, and they show girls that girl power isn’t just one thing."
Be true to you: "Just like Nicki and Isabel use girl power differently, their interests, friends, and hobbies are unique, and that’s okay! When Isabel gets kicked out of the Millennium Party dance with her friends and Nicki feels too shy to talk to the “cool skater kids,” they both learn that the most important thing is for them to be true to who they are—no matter what anyone else, including their twin, thinks."
Face your fears: "Isabel and Nicki add “conquer a fear” to their Y2K countdown list, and it pushes them to support one another in facing their fears. Whether that’s visiting the top of the Space Needle or trying a skateboard trick in front of new friends, the twins find that fears are easier to face when you have support from those around you."