While I still haven't worked out exactly what the minimum requirements are I do know that if you want to be there for her you must have chosen to try to save her from falling. In order to choose to save her you must have (once again I'm still not sure which) either a certain level of Love/Lust, or completed X number of Lindsey Quests. As soon as Season 2 starts and you have finished your first visit to Homeroom all you have to do is wait a week and the Quest "Touched by an Angel" will automatically start.
Good luck and hope you continue to enjoy the game! :)