I read this in 90s but the book might've come out in the 80s.
A girl at her library finds a how-to book about witchcraft in the children's section, among other how-to books. She's been at this library her whole life and never saw it before, so it catches her eye.
She, her guy friend, and her little sister, all learn about spells but in their specific way. The main character about nature, the guy friend about machinery/mechanics, and the little sister on a Mac (non Mac, no bite out of the apple).
They save the world in various ways. Once by traveling through space, once in the ocean shape-shifting into I think dolphins, meeting a shark and they have to do a play with specific parts. The shark takes the main characters place for her role in a dramatic turn later.
I'd like my daughter to read it, but have no idea the author or book title.
Thanks in advance for any help!