Looking for a book of short middle grade ghost stories read in 80s (so possibly 70s/80s book). Boy attends school in London and meets a girl who is revealed to be a ghost and had been killed by a bomb. Possibly a timeslip situation where he tries to save her or maybe she saves kids at the school from a fire? Not Kept In Timperley I think it is mentioned she was killed by a doodlebug, but not sure on that. Thanks!