Exactly. Removing Alicent from the room is an odd choice to me, because not only does witnessing this horrible event with her own eyes make it even more personal to her, but she would've also been a good POV character alongside Helaena there for the audience. The actress did a good job, and she played the scene true to Helaena, but the character is naturally distant and ethereal, and her line readings didn't necessarily sell the horror of the situation in the same way Alicent could've, much like Catelyn in the Red Wedding.