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Despite her mom leaving rehab last week, Rumer Willis managed to put on a happy face -- and a skin-tight dress -- for the Diary of Preston Plummer premiere on Monday evening in Miami.

At the event, the 23-year-old worked one of Herve Leger's signature, cleavage-baring bandage-style dresses.

Even though her hair was done up in a romantic low chignon, the star kept things edgy with her shoes -- black sandals -- and her makeup -- bright red lipstick and black nail polish.

Following her Jan. 23 collapse, Willis' mom, Demi Moore, checked into Cirque Lodge in Sundance, Utah where she stayed until she left for a vacation at Parrot Cay in Turks and Caicos late last month.

"She knows she's in a bad place and needs help," a source explained to Us Weekly in January of Moore, 49, who first went to rehab in 1985. "She needed something serious to get her back on track."