If you didn't get the "Invite Up" message from Kelly, you haven't hit on her enough. You have to keeping asking her "how she feels, We will, and then I'd Embrace You." Do that enough times after the suicide mission, granted you saved her, and check your messages. You'll eventually get her message to invite her up. Make sure you denied each girl their love for you. That's a major key to get Kelly to send you the message.