Marnie, the Shih Tzu whose lolling tongue, amused expression and tilted gait made her a star on Instagram, died on Thursday at her l. a. home. She was 18.

“She passed very, very peacefully,” said Shirley Braha, who adopted Marnie from a Connecticut shelter in 2012. “She gave up the ghost of adulthood is that the easiest method to place it.”

Marnie’s quizzical face and uncanny gift for posing garnered 1.8 million followers on Instagram and turned her from a dirty rescue dog into a billboard pet for adopting older animals.

She posed with the likes of Katy Perry, Tina Fey and Selena Gomez; got a book deal; and at one point became so famous that her absence at the 2015 World Dog Awards made headlines on TMZ....