In the book "Fangirl" by Rainbow Rowell the author focuses more on the theme of isolation and family. At first Cath and Wren are inseparable, always together no matter what but as they start to grow up Wren starts to outgrow all her "childish" ways and leaves Cath behind, especially now that they are off to college together. Wren decides to focus more on having a good time and partying while Cath decides to stay isolated in her room becoming more anti-social. Growing up means facing more challenges and coming out of your shell is just one of those challenges. But if you go into more depth, you might realize that Wren is also facing her own challenges. Being left by your mom at such a young age can be very challenging and maybe by holding on to her sister it just meant holding on to the past. Being so close to her sister and dad every day reminded her of all that so by going to college and getting a different roommate it only meant that she wanted to get away of all the sorrow for a bit.