Click http://www.catholic.org/saints/stindex.php
and a link will take you to a list of all the saints. Once there, click on 'R' for those with names beginning with that letter. You will find that the closest thing to 'Rachel' is 'Rachilidis'. So, sadly, it would appear that there is no true St Rachel, though I believe the title has been given to some woman who led an anti-war protest!