[From Forebears Research] -- The Toronto Police Archives (accessible through the Metro Police I believe) should be able to help. If she was a minor, then the Children's Aid currently may know what existed then in this capacity. Beyond that, if she was found dead at some point there should be a coroner's report. There may be some school records from the time that could have useful details although not specifically to do with the search, rather info on her personally.
You should also check the newspapers in the area where she resided in 1891, as well obituaries, wills and other such events of the remaining family members.