The Girl with the Glass Bird by Esme Kerr

When feisty Edie is sent to a remote school to spy on fragile Anastasia, she never imagines that they'll become best friends instead--and discover an ominous plot that puts both their lives in danger!Through a series of strange coincidences, orphan Edie finds herself at Knight's Haddon, a stately boarding school for girls. But Edie is not just another student--under normal circumstances, she could never afford to go to boarding school. She's been sent to Knight's Haddon by her art-dealer uncle to investigate the disappearance of a precious crystal bird that belongs to his secretive client's daughter. Anastasia, a Russian royal, has a fragile disposition and a melodramatic bent--or so the headmistress and all the other girls say. Edie's assignment is not only to find the missing glass bird; it's to befriend the troubled blueblood and keep a watchful eye on her. When the two girls uncover a dangerous plot, how can they stop it? Inside the walls of the isolated estate, is there anyone they can trust?