Big Summer by Jennifer Weiner

 Daphne is a moderately successful blogger and babysitter in NYC, and has been obsessed with her weight all her life. She lives with a good friend (Darshi) from the ritzy high school where Daph was a scholarship student. And she has an on again/off again relationship with her frenemy Drue Cavanaugh.

Drue is rich and beautiful and entitled--everything Daphne is not. So whenever Drue allows Daphne in her orbit, Daph is excessively grateful--until Drue screws her over. Because Drue is basically not a nice person. After one particularly cruel stunt, Daphne leaves Drue behind for good. Then years later, out of the blue, Drue tries contacting Daphne, who ignores her, until she ambushes Daph at the home where she's babysitting (and I wish we had spent more time with the little boy Daph babysits, who was adorable). Anyway, Drue begs Daphne to forgive her--and to be a bridesmaid in her upcoming wedding because it turns out she doesn't really have any friends. Daphne eventually succumbs to Drue's pleas and heads off to Cape Cod for the social event of the season--much to the delight of her boss, Leela, who thinks the media (and social media attention) will be great for their brand. 

When something happens to Drue the night before the wedding, Daph becomes a suspect--along with the hunky guy she met at the rehearsal dinner, who has mysteriously vanished. Daphne and Darshi (who also got burned by Drue in high school) try to figure out what really happened the night before the wedding and find out a lot more about Drue than they ever knew before.

It was an interesting look at friendships and families--and whether or not someone can really change.