At camp in the film, Bridget and Eric race and discuss how great running feels. Bridget says "It's like you're just in this place where nothing bad could ever happen, you know?" Earlier in Carmen's opening narration, we see the girls at Bridget's mother's funeral. When it's over, she tells her friends with a smile that she'll run home.
Someone on IMDb's board for this movie pointed out how the four girls represent the four kinds of Greek love:
Bridget- Eros, erotic love. She deeply desires Eric and ends up having sex with him.
Lena- Storge, romantic love. She experiences romance for the first time and it's the theme of all her storylines.
Tibby- Agape, unconditional love. Bailey teaches her about self-giving love and looking at other people without so much cynicism.
Carmen- Philos, familial love. Carmen works out her issues with her father, forgives him and accepts her new stepfamily.
Fridge Logic
Sisterhood Everlasting handles a particular plot point in Tibby's storyline very strangely, specifically her apparent diagnosis with Huntington's disease. Putting aside the fact that the timeline doesn't make a lot of sense, Huntington's is genetic, meaning Tibby had to have inherited it, and she has two younger siblings who would also be at risk. Tibby's daughter Bailey is specifically noted to have not inherited the gene for Huntington's, but no one at any point mentions that someone probably needs to tell Tibby's parents the truth so that they can get their other children tested.
for this movie pointed out how the four girls represent the four kinds of Greek love: