So, I think I did everything right before the attack on the citadel by Cerberus.
I got the scene where she sat on Shepard's lap, and said the best options available to me when she brings the time capsule to Shepard's quarters.
Now, just after the citadel mission, i have had a few opportunities with other crew members, but i didn't receive a message from Liara about talking to her on the citadel. Does this happen at a later point?
It should happen after a couple missions after the Cerberus Attack on the Citadel. If I remember correctly, her scene is a bit later than everyone else. --- "With kindness comes naivete. Courage becomes foolhardiness. And dedication has no reward..."
i am fairly certain all the romance "locking" scenes take place after the cerberus attack on the citadel. there are a few "flirting" scenes before, but the actual romance starters come after. --- it's not easy being this awesome and modest