Everyone bitches at the movie industry for screwing up popular books, but Hollywood never gets nearly enough credit for the times it improves upon popular books. Remember how Robert James Waller’s The Bridges of Madison County was a painfully earnest weeper of a novel, but was turned by director Clint Eastwood and screenwriter Richard LaGravenese into an achingly poignant movie? That was awesome. Remember how Tolkien’s The Lord of the Rings was a stiffly-written epic before Peter Jackson transformed it into something poetic in its magnificence? That was even more awesome.

So sometimes a screenwriter can make things better. And sometimes a screenwriter can make some things better, while making other things worse. And when the latter happens, you end up with something as satisfying and frustrating as In Her Shoes.

Jennifer Weiner’s 2002 novel became a hit with the chick-lit crowd for its tragi-comic take on the contentious relationship between two adult sisters. Rose Feller (Toni Collette) is a successful Philadelphia attorney, but a plain Jane whose romantic life consists of novels with pictures of Fabio on the cover. Her sister Maggie (Cameron Diaz), on the other hand, has never had trouble landing guys, but her learning disabilities have made landing a steady job considerably more difficult.

Rose has always bailed Maggie out of the ongoing disaster that is her life, but when Maggie goes one step too far and enrages Rose, she’s left without her safety net. Desperate for somewhere to go, she turns to Ella (Shirley MacLaine), the retired grandmother whose existence had been hidden from the Feller girls for years by their widowed father (Ken Howard).

Grandma Ella doesn’t make her first appearance in the film until around the 45-minute mark, and that’s just one place where screenwriter Susannah Grant (Erin Brockovich) considerably streamlines Weiner’s narrative. Most notably absent is an extended section where Maggie stows away in the library of Rose’s alma mater Princeton, and it’s a savvy decision. Weiner makes a huge point of having the two sisters essentially exchange lives after their falling out--Maggie attending college classes, Rose dropping out of professional life and getting a boyfriend (Mark Feuerstein)--and the juxtaposition clearly looks forced after Grant’s concise fix. The film may lose the double-meaning of the title--Maggie and Rose metaphorically seeing life through each other’s eyes in addition to sharing footwear--but it also loses a lot of flab.

Meanwhile, it also loses a lot of sisterly connection. Grant makes some significant changes by revealing details about the sisters’ childhood and their relationship with their dead mother much later in the story, details crucial for establishing the bond that connects them in spite of their polar-opposite personalities. While Collette and Diaz both deliver fine performances--the latter in particular as she wrestles with her sense of self-worth--it’s harder to get a sense of what unites them when the story separates them for much of the running time.

That tension between smart choices and confounding ones runs through nearly all of In Her Shoes. Director Curtis Hanson (L.A. Confidential) directs at times with a restraint uncommon to chick flicks, yet also chooses to underline the opening scene (by scoring it to Garbage’s “Stupid Girl”) and the closing scene (by repeating a poem for emphasis). There’s a great casting choice in Feuerstein as Rose’s no-nonsense Prince Charming--he does a priceless reading from one of Rose’s bodice-rippers--and a terrible casing choice of the always-imperious MacLaine in a role that demands a deeply introverted sense of grief. It will earn the honest throat lumps of a scene in which Maggie has an epiphany about her own intelligence, and then stumble into confessional confrontations dripping with melodrama.

Perhaps it’s enough that In Her Shoes is better than a lot of similar fare--you know, the kind of fried green ya-ya movies that seem like they’re released into theaters simply as precursor to the inevitable ad nauseam run on Oxygen and/or Lifetime two years hence. That’s the kind of story it was in Jennifer Weiner’s book, and Susannah Grant has adapted it into something more artfully structured. Simultaneously--and perhaps ironically--she may also have made it something less purely emotional by taking some of the chick out of the lit.