I was able to get this achievement during the Solo story (and not Curator's Cut either). A few things to note: (If you've played the entire game through once, just select the UNINVITED GUESTS chapter to get started on this achievement- it should save some time!)
-First, Fliss needs to successfully flirt with Conrad when controlling her for the first time. When choosing her dialogue, choose RELAXED, SELF-ASSURED, and then IMPRESSED. After that, proceed to go over to Conrad and continue the conversation. For the next set of dialogue, choose RELAXED, PLAYFUL, and then ROMANTIC.
-Second, Conrad needs to stay with the group when the pirates attack the boat. I personally recommend that you have Conrad try and escape in the speedboat and then intentionally fail the QTEs (an easy way to do this is just let the time run out for the 1st QTE). I'd also recommend that you keep Brad hidden.
-Third, when everyone gets on the ship, you'll be controlling Conrad. Once the group is put into the room, a conversation will start. When Conrad has his dialogue, choose PUZZLED, APPROVING, and then CURIOUS. After that, choose ANXIOUS when discussing the escape route, choose to DISTRACT the pirates, and REPLACE the desk to ensure that Fliss stays with the group.
-Lastly, when the group hides from the pirates as they enter below, Fliss will notice the distributor cap. As Conrad, choose the SELF-ASSURED dialogue. The achievement should then pop!