Police say she entered the Circle K just after midnight, implied she had a gun and demanded money. She fled on foot with an undisclosed amount of cash from the register.
Police say the suspect is 20 to 30 years old, reports KEPR-TV News.
In addition to the fake whiskers, The Tri-City Herald reports, she also spoke in a low voice.
Anyone with information is asked to call Kennewick police.