Once you complete the prologue of Baldur's Gate 3, you're thrown onto a beach surrounded by the debris of the Nautiloid that you woke up on and by the victims of the Mind Flayers that captured you. Assuming you freed Shadowheart from the pod in the Nautiloid you'll find her among these corpses, only she's less a corpse and more just an unconscious person, and you're given a few different choices on how to proceed from here.
Should you take the artifact off Shadowheart?
You can either leave Shadowheart where she is and not bother recruiting her (yet), you can wake her up so that you can journey through the land of Faerun with her or you can try and take the artifact that she's holding her in her hand for yourself. If you try and take the artifact, however, Shadowheart will wake up and immediately distrust you, causing her to already have a negative opinion towards you as you start your journey through these dangerous lands.
Due to this, we'd recommend just waking her up. It's not worth starting the adventure with a negative companion, and it could make certain story events later in the game a lot harder since she won't like you and she won't trust you, and romancing her becomes exponentially more difficult.