Accidental demons

"For the youngest in a long line of witches, demons used to be no big deal. A spell and a quick prick of the finger, and a witch like Ber could summon a demon to do anything she needed--clean a mess, send a message, you name it. But that was before Ber was diagnosed with diabetes. Now each time she tests her blood sugar, accidental demons are slipping into the human dimension . . . and causing absolute chaos. Good thing Ber and her older sister, Maeve, know that every magical problem has a magical solution. They'll just conjure a low-order demon to monitor her blood sugar! Bonus: they only have to bend one or two teeny, tiny rules. But before they know it, they've stumbled into deeper, more mysterious magic than they ever could have predicted. And soon it's not just Ber's magic but her entire coven that's in danger"--Provided by publisher.