In “Sherrybaby,” which makes its premiere tonight, Maggie Gyllenhaal plays the title character, and just like Julia Roberts in “Erin Brockovich,” she sets out on a scantily clad expedition to exceed preconceived notions about herself. But “Sherrybaby” is everything that “Erin Brockovich” was not. Thanks mostly to the tumultuous performance of Ms. Gyllenhaal, it is a much more realistic portrayal of someone struggling against the constraints of low expectation.

Though she may be an ex-con and former heroin addict, Sherry is determined to straighten out her life and raise her daughter Alexis (Ryan Simpkins). In prison, Sherry found God and sobered up. She returns home after three years, expecting to rehabilitate her relationship with her daughter.

But her family does not seem confident in her transformation and it soon becomes clear that her brother Bobby (Brad William Henke) and his wife Lynette (Bridget Barkan) would like to raise Alexis as their own child.

In addition, Sherry’s parole officer seems set against her, a woman at her halfway house has it in for her, and her father seems to have abused their relationship more than once.

Despite these setbacks and the general difficulties of succeeding as a former convict, however, Sherry seems to have a shaky grasp on navigating the pitfalls of her life outside of prison, until it becomes all too clear that she is not in control at all.

At some point in “Sherrybaby,” second-time director Laura Collyer allows the tight focus on Sherry’s point of view to broaden. Although Sherry thinks the world is set against her — and at times it is — it soon becomes clear that she may not have the life skills to make it on her own or as a mother.

Suddenly, her brother’s wife doesn’t seem like such a monster for trying to protect Alexis from her own mother. And just as every corner may hide someone looking to take advantage of her, it becomes increasingly unclear if Sherry can stop herself from making bad decisions.

While it is endearing to watch someone turn her life around for the sake of a child, it is nevertheless difficult to watch someone who — despite a strong desire to do right — just can’t cut it. “Sherrybaby” balances the action between these two options for most of the film.

What keeps it all from falling into melodrama is Ms. Gyllenhaal’s depiction of Sherry as a sometimes winning, but ultimately flawed character who can’t distinguish what she wants from what she is capable of.

Ms. Gyllenhaal possesses an unconventional attractiveness, and though she can appear stunning, she can also look like an exceedingly normal person — a dwindling commodity in young Hollywood talents.

Most important, she has the ability to completely lose herself in a character, which is precisely what she does here. Ms. Gyllenhaal’s performance is riveting, emotional, and at times, a little frightening. It is hard not to root for Sherry, as Ms. Gyllenhaal imbues her with an endearing, but shaky confidence.

As she continues to flirt with disaster, it seems clear that Sherry’s center cannot hold. She has some understanding of how thoroughly she has let her child and her family down, but she doesn’t have the capability to improve her behavior. Alexis seems to have been a sobering consequence of rampant promiscuity, but as soon as Sherry gets out of jail, she resumes every addictive behavior available, excluding drug use. But even that never seems far off, and sometimes it isn’t.

While she wants to protect Alexis from the pitfalls that befell her young life, Sherry may only be introducing new ways of hurting her young daughter. She wants desperately to regain some semblance of control over the chaos that is her life and gain the respect of her family, but unwilling to take steps toward reform, Sherry increasingly seems more like a pawn than a player.

“Sherrybaby” often veers close to the pitfalls of a movie of the week, but the film acknowledges that even though the audience may want someone battling her demons to beat the odds and turn her life around, there is no guarantee that she will succeed.