Kelly Rutherford's not worried about Taylor Momsen, crazy antics or not.

On Gossip Girl, Rutherford, 42, played stepmom to Momsen's Jenny Humphrey -- until the 17-year-old was asked to leave the show last month for an indefinite hiatus.

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But Rutherford told HollywoodLife that Momsen has just shifted her focus from acting to music (Momsen fronts the band Pretty Reckless.)

"Her passion has just really become her music," Rutherford said. "Taylor's out there doing her music and if you hear her music you understand why she is so passionate."

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Still, Momsen's departure from the show coincided with her increasingly dark reputation: the former kid star has flashed her breasts to a concert crowd, given countless potty-mouthed interviews and even requested a full bar on her tour rider despite being underage.

"I think she's young," Rutherford said. "And is exploring her world and she's exploring being an artist. I think it's important to be fully expressed."

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"She works hard on Gossip Girl but doesn't care about the plot or the other cast members," a Momsen source recently told Us. "She treats it like a 9-5. No emotional investment."

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