The stepdaughter turns her back, while the stepson eagerly returns a hug. The stepfather gets a kiss when he drops the kids off, the stepmother rates only a half-hearted wave.

There's no playbook for women who marry into stepmotherhood.

"You walk on eggshells when you're a stepparent," said Lynnae Haines, a Richfield stepmother of a teenage girl and a member of the Twin Cities Stepmom Meetup group.

From the gripping testimony of Amy Senser's stepdaughter to the new remakes of the Snow White movie, unavoidable drama and deep cultural archetypes are at play in the relationship between stepmothers and stepdaughters.

"The research is clear," said William Doherty, professor of Family Social Science at the University of Minnesota. "Stepfamily relationships are incredibly complex, and the trickiest is between stepmother and stepdaughter."

That's partly because most contemporary stepmothers must also deal with their husband's ex-wife. Even if the two women never cross paths, the biological mother's presence is almost always a constant in a stepmother's life.

"Historically, stepfamilies were formed by death. Now they're formed by divorce," said Doherty. "That means another parent is still around, complicating things."

Conflicting loyalties

What psychologists term "loyalty conflicts" can be triggered in children when a parent remarries. Painful, persistent and often unconscious, the conflict is especially potent in stepdaughters.

"The loyalty conflict is the daughter's feeling that she betrays her mother if she loves, or likes, or maybe even looks at her stepmother," said Wednesday Martin, a New York stepmother, social researcher and author of "Stepmonster: A New Look at Why Real Stepmothers Think, Feel, and Act the Way We Do."

She quotes a 30-year study on post-divorce life from the University of Virginia that suggests that girls typically identify with their mothers after a divorce.

"Stepdaughters feel like they have to be on Mom's team," said Ann Orchard, an Edina stepmother and psychologist who led a stepmothers group for 10 years. "They feel they must represent Mom's agenda in Dad's house."

"In some cases, the mother coaches her daughter to create conflict," said Martin. "Sometimes the mother is ambivalent or silent, and the girl draws her own conclusion, which is 'It will destroy my mother if I have any sort of a relationship with my stepmother.'"

The conflict can take a lifelong toll, creating tension in father-daughter relationships and stress in both homes.

'This is human nature," Doherty added. "This is hard-wired, core stuff. People can't reason their way out of it."

Aid from adults

Loyalty conflicts can be eased, but it requires effort by the adults, who may be challenged by the bitterness and blame that often follow divorce and remarriage.

"The kindest thing a mother can do is explicitly release the girl from the loyalty bind she's locked in," Martin explained. "Her mother must tell her, 'It's OK with me if you give your stepmother a chance.' The resentment de-escalates and allows the girl to have healthy relationships in her father's home."

That may be harder than it sounds.

"It takes a special mother to be secure enough and mature enough to do it," said Orchard. "But the biological bond is so tight, they shouldn't worry. A stepmother can't threaten their connection with their daughter."

Fathers, too, have a critical role in minimizing the loyalty conflict. Martin said he must support his new wife without criticizing his ex-wife. In an oh-so-delicate shift, he can demonstrate that in order for his daughter to be loyal to him, she must be civil to her stepmother.

"The dad must claim his wife as his partner," said Martin. "He must say, 'She's here to stay. You don't have to love her or even like her. But you may not treat her like furniture.'"

In her workshops, blog and book, Martin continually reminds stepmothers that they need not feel maternal in order to have a successful relationship with stepchildren.

"Everyone's watched 'The Brady Bunch' and thinks if you love them, they'll love you back," said Martin. "When that doesn't happen, there's guilt and shame for the stepmother. Even her husband might blame her."

In her groups, Orchard has advised stepmothers to approach stepchildren with the expectations they held when they met their college roommate.

"You didn't like that person as soon as you met and you didn't expect to. Sometimes you become close, but you can also have a solid relationship without that."

The measure of success in the relationship can be simply coexisting.

"Stepmothers can't say it often enough: 'I'm not trying to be your mom,'" Martin added. "Changing the expectations reduces the pressure -- on everyone."

Kevyn Burger of Minneapolis is a broadcaster, podcaster and freelance writer.