Audio problem: When Miss Irvine is sitting the room alone after being ejected from the banquet, she says that she never wanted to be one of them but her mouth doesn't move. (01:17:31)
Audio problem: Bruno's mouth is out of sync when he says "I really do hate margarine," as he is talking to the waitress about what are in the sandwiches that day.
Audio problem: When Mr. Stringer says "What the devil," as all of the sheets of paper on the reception desk start flying about, his mouth doesn't move.
Audio problem: Near the beginning, after Erica disappears and Helga visits Erica's mother, Erica's mother says "Come on in Helga, have some cake", but she is clearly saying something else.
Audio problem: When Luke (as a mouse) finds Formula 86, we hear him say, "We got it, Grandma," but his mouth doesn't move.
Answer: She probably didn't know about her master plan, just about turning kids into mice. Most likely she thought they'd be kept in locked cages and held prisoners.
During the meeting, Miss Ernst says that every child in England must be "Rubbed out. Destroyed." A clear indication that she was talking about killing the children after they get turned into mice but, Miss Irvine doesn't seem shocked or upset after hearing this.