Absentee co-worker

I need help on what to do. Have a coworker who consistently calls in for her shifts. It's gotten to the point where other coworkers don't want to pick up her hours and/or considering other jobs. When she is here, she does bare minimum. I have an urge to write our boss, voicing my concerns. Do I? I don't want the good staff to quit, and feel like I should of said something. She's called in 5/7 shifts just these past 2 weeks!!