Sophie has often looked uncharacteristically as if she is looking sternly at people this past week. I think it is just her trying to contain her profound grief / mask her emotions as she was very close to the Queen. I don’t think she is cross, just very upset and trying to hold it together in public.
In the picture of her looking in Catherine’s direction I notice her husband Edward, next to her, is looking to the left the same as her - as is William, slightly, on her other side. Maybe they are all looking down the aisle at something/somebody?
I also think an older person somewhat behind Princess Catherine had to leave their seat and exit the area during one of the sermons. I didn't get to see who it was. Maybe she heard a bit of commotion from that.