If you weren't watching closely, you may have missed that every time Anna goes to visit Elizabeth's grave, the inscription on the headstone is different. It's a subtle way of establishing Anna as an unreliable narrator — showing that even when she's acting lucid, she's not seeing things as they really are. In the first episode, the headstone reads, "If love could have saved you, you would have lived forever." In the second, it says, "In heaven, you can dance like no one's watching." And the last time we see Anna visit Elizabeth's grave, the headstone reads, "There's no 'I' in heaven."
Were any of these the real inscription? Earlier in episode six, Anna flushes all of her pills and pours all her wine down the sink, but we don't know exactly how much time passes between when she does that and when she visits the grave. So even though we know she's no longer drinking or taking her prescriptions, the psychotropics that Douglas prescribed probably haven't worked their way out of her system just yet — leaving us to wonder just what that headstone actually says, and why Anna doesn't seem ready to see it.
