The Stig / Splash News 1 / 19
The Stig / Splash News 1 / 19

Given all that her family has gone through in the last few weeks, it was time Tallulah Willis had a chance to unwind.

Celebrating her 18th birthday at the Beverly Hills, Calif., home of her dad Bruce Willis, Tallulah donned a tiara, white tank top and cutoff jean shorts to host a low-key bash for friends Friday.

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Though mom Demi Moore -- who was hospitalized Jan. 23 after suffering a seizure -- was nowhere in sight, Tallulah's older sister, Rumer, 23, stopped by for the party. The girls' 20-year-old sister, Scout, is away studying at Rhode Island's Brown University.

Tallulah has been staying with her dad Bruce -- currently expecting his first child with new wife Emma Hemming -- since her mom's medical emergency.

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"Things have been strained between Demi and [daughter] Scout and Tallulah for a long time," a source tells the new issue of Us Weekly. "For a while, Ashton [Kutcher] was acting as the primary parent because Demi was so out of control."

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As Moore recovers, Tallulah's father has begun to back away from his ex-wife. "Bruce and Emma made a conscious effort to distance themselves from Demi," a family source explains. "She's not a good influence, and Bruce and Emma want to keep things healthy."