A complete list of when and how many times you need to talk to Lucy in order to get the achievement. You need to speak with her all of these times in the SAME playthrough, so make sure you don't miss any or you'll have to start a brand new game.
First Time – Is right at the end of Memory Block One (the first time you’re pulled out of the Animus). You must talk with her twice; press any button to begin the conversation.
Second Time – At the end of Memory Block Two (after you have assassinated your first main target). You must talk with Lucy three times here.
Third Time – Is at the end of Memory Block Three. You must talk with Lucy twice.
Fourth Time – Is at the end of Memory Block Four. You only need to speak with her once here. Note: This conversation is automatic, you don’t need to press any buttons to initiate it.
Fifth Time – You need to talk with Lucy once again at the end of Memory Block Five. You have to speak with her three times.
Final Time – The last time you need to speak with her is after you have slain your last target, or Memory Block Six. You must only speak with her once.
You should now get the achievement!