Murder is Elementary (Susan Wiles Schoolhouse Mystery Book 1) by Diane Weiner

Susan Wiles is blissfully retired from her career as a music teacher. What a joy to be able to attend the holiday concert without worrying about how her chorus will perform. But wait. Where's the principal? Susan offers to check, only to find the principal lying dead on her office floor. Of course, now that she's retired she has time to help the local police (one of whom is her daughter) solve the mysterious crime. Did the principal die of natural causes? The bruise on her face doesn't seem severe enough to be fatal. What about that funfetti cupcake sitting on her desk? Could she have been poisoned? Susan has just found the perfect retirement activity, much to her daughter's chagrin. And when the principal's teenage daughter, one of Susan's all time favorite students, asks for help - how can she say no? Little does she realize that this crime will take her far from the schoolhouse doors, as she investigates a mystery that extends back into one family's painful past.