Please Don't Tell My Parents I'm a Giant Monster

When an evil artifact offers you the power to turn into a monster, agreeing would be stupid. Mirabelle isn't stupid. She also doesn't have much choice. Her friends all have super powers that let them go on exciting adventures. Mirabelle's super power is to be made of glass, and walking across a room is dangerous enough.But the shiny rock won't shut up, and to get rid of it, she has to use its powe...