You should just go talk to Serena at Day or Dusk in the Science Classroom (you can access it through the Hallway).
And the easiest way to currently meet Jennifer is in the courtyard during the weekend mornings.
A guide sounds like a good idea, but I'll have to leave it for the community to write one, sorry :D I barely have enough time to actually work on the game itself. I might have a better way to track the girls in the game eventually, but not yet.