Ghost Problem with sims 3!! someone help me!!?

one of my sims died so i put her grave in the back garden and she suddenly became a ghost! its weird coz i cant control her but she hangs around my house and uses the facilities.! when i try to delete her grave it says that i cant, and i also cant take her to the cemetery because i cant pick up the grave! Someone please help me she is annoying the heck out of me and i really need her to go away!!