Hanahope, I would highly recommend YA Historical fiction like "The Luxe" (Amazon: "Gossip Girl meets the Gilded Age") and "Bright Young Things" (1920s NYC flappers) by Anna Godbersen as well as "The Divas" (1920s series set on Long Island) by Jillian Larkin.
Also the two-book series by Ann M. Martin and Paula Danziger (P.S. Longer Letter Later and Snail Mail No More) novels in letters and emails between two best friends when one moves away, (Warning: there are some serious topics discussed here and there in the books, alcoholic father, parents separating etc., but ultimately are uplifting, with many great moments of friendship between the two girls.
Enough can't be said about all of Danziger's books, love them and re-read them all the time, Can You Sue Your Parents for Malpractice?, The Cat Ate My Gymsuit and follow-up There's a Bat in Bunk Five, and This Place Has No Atmosphere (set future where teenage girl moves to the moon with her family) are my faves.
Cynthia Voigt is also really good, esp the Tillerman cycle, which starts with Homecoming and Dicey's Song...
Will echo suggestions for non-sci-fi fiction by Madeleine L'Engle, love the Austin books as well as And Both Were Young. Same with Little Women and Little Men etc.
I also really liked The Future of Us, where a high school girl in the mid-90s can see her (and her friends') future Facebook pages via an America Online disk (remember those???) she receives in the mail. She tries to change the future based on the info she discovers about the future.