I come across this from time to time - example today "Helen O'Brien". She is on my watchlist, so definitely part of Wikitree, but does not appear??
"Sorry, but no matches were found for "Helen O'Brien "."
Thanks,
Steve
When you type O'Brien in the surname search box, and then resort them alphabetically to find the Helen's she is there?
http://www.wikitree.com/index.php?title=Special:Surname&s=O_BRIEN&order=name&u=