A young woman who volunteered to lead her Mexican hometown's police department after a predecessor was beheaded by drug gangs has fled her post to seek asylum in the U.S., authorities said Tuesday.

Marisol Valles was declared in headlines "The Bravest Woman in Mexico" when she took the job in the Mexican town of Práxedis G. Guerrero last year. Now, she is seeking asylum near El Paso, Texas, said Gustavo de la Rosa, the human-rights ombudsman in the Mexican state of Chihuahua where Práxedis is located. Ms. Valles couldn't be...