Spoilers! (Sorry)
First of all, the "horrible decision" made by the older sister Meaghan during her young adulthood, was basically the decision she made to go to college and pursue an education/career and try to make something else of her life. It was not a horrible decision, and the book tries it's best to paint what she did as something awful and regretful. She gets vilified for it, not only by most people around her, but the pressure and guilt that she puts onto herself about what happened is pretty sad. When you know her backstory, her "horrible decision" kind of makes sense, I don't really blame her for going that route. The whole premise of the book is based around this plot point, and it makes no sense once you get to know the characters and the history. So this was frustrating throughout the book.
The book itself was a fairly easy read. Enjoyable, but pretty melodramatic and unrealistic.
I was Team Meaghan throughout. Although her psychiatrist visits and one night stand behavior was a bit over the top. The basic intentions behind her lifestyle and personality were pretty understandable when you figure out what happened in her childhood. Meaghan actually had the biggest character arch, and had the most emotional growth of all the people. In the relationship with her sister Claire, Meg did ALL of the work in mending the fences.
Her character was set up to be the "bad one", who needed to see the light and change everything about herself. Throughout the story, she was judged pretty harshly by Claire, Claire's friends, Claire's dad, their horrible mom, and a lot of others. But it was Meg that actually took the giant step to make an effort to rekindle the relationship. She was going through a ton of stress and drama in her own life after almost being killed by a clients husband. She never asked anyone for help or support, other than her psychiatrist. But was expected to be the support system for everyone.
Meg planned (and paid for) Claire's entire wedding, even when she didn't totally agree with the marriage, she attempted to play along with all of the wedding hoopla even though she was out of her comfort zone in small town Claire's circle. She watched Claire's daughter while they were on their honeymoon. When Claire got sick, it was Meg who stepped up and took care of her and basically saved her life by being relentless in seeking treatment. Meaghan was the rock and the MVP of the book, and got a lot of hate for it, even though she came full circle and figured out what was needed mentally and emotionally in her life.
Claire was set up to be the sweet sister, who the reader is supposed to really fall in love with and rally behind. Her character kind of fell flat. To me she was pretty childish, needy, and quite frankly very selfish. She was also a bit slow, for lack of a better word. I think this was an attempt to portray her as endearingly sweet, kind, unselfish, and caring. For some reason, she was universally loved and praised by everyone around her. Also, quite coddled. But she didn't actually do anything in the story to warrant that love. Claire was all about Claire.
Her storyline was the most unrealistic. She falls in love with a man, and decides to get married after a few weeks. The guy somehow just inserts himself into her life and family, with no issues. None of her close friends or family questioned the relationship or voiced any concerns? Time to start thinking about who your friends are. But Meg gets lambasted for even daring think about it practically, give her some suggestions, or even just question the motives. Then there is Claire's princess fairytale wedding and honeymoon, followed by the brain tumor 3rd act. Again, Claire can't handle anything herself. She depends on Meg to lift her up and do everything, meanwhile making her feel guilty when she says the wrong thing or is too harsh or blunt, or makes any misstep that isn't the way Claire would do things. Claire literally put in zero effort in fixing the sister relationship, but still expected the world of Meg.
Claire spends the entire book trying to come to terms with Meaghan's "abandonment" of her when they were younger. When that didn't happen. Claire was safely in the care of her biological father at that point, and well loved and supported. Her struggle as a child was hardly as difficult as her sister's. Meg was a teenager, put in an awkward position of having no mother or father, and didn't know how to transition to life with Sam. So, she acted like a teenager. And eventually moved on to college, while trying to build her own life.
Claire never had the appropriate ah-ha moment of realizing: "Oh God, my older sister sacrificed her own childhood to raise me, then had to figure out where she stood once my own dad came into my life, and was young and scared and didn't know how to handle the situation so made some teenage mistakes. Then eventually decided to go to college, and seek out her own opportunities while knowing that I was now in a safe and stable place."
For being such a sweet, down-to-earth, amazing, strong, woman, Claire was never able to put herself in her sister's shoes at all, even at the age of 35. She never understood why Meg didn't want to stay with her and her bio dad as a young adult. Meg was able to rise above a lot of struggles and make something of herself (yes, she had many emotional issues along he way because of it), but still pretty admirable what she was able to do. Claire always just saw the "abandonment" and nothing else. How about blaming your horrible mother for that? She was actually the real villain of the story (yet painted as a quirky, endearing actress). Even her Dad Sam had his sweet moment with Meg when they both acknowledged what happened in the past, and explained their mindset at that time things happened.
Then there is Joe, the depressed vagrant who is actually a grief stricken, disgraced former superstar radiologist. Although I kind of liked his character in the mix, I couldn't help but role my eyes at the premise. Also Claire's husband Bobby, who is basically an NPC with a guitar and unrealistic country star side story. And Claire's daughter Ali, who just kind of goes along with her new dad and all the other stuff without any issues.
Finally, I have to mention the places in the book where the women dramatically interrupt all of the doctors and specialist, mid sentence, because they don't want to hear what they have to say. They even do this to the "good" doctors that saved Claire's life. Because they are now "strong and fearless" warriors, and finally Claire has found her voice. No honey, please just listen to the doctors. They are saying some important things, and it won't take away from your new found fierceness.