Winifred: Oh, look. Another glorious morning. Makes me sick!
Winifred: You know, I've always wanted a child. And now I think I'll have one on toast!
Emily: Thackery Binx, what took thee so long?
Thackery Binx: I'm sorry, Emily. I had to wait three hundred years for a virgin to light a candle.
Billy Butcherson: Go to hell!
Winifred: Oh! I've been there, thank you. I found it quite lovely.
Answer: They were set up, beforehand, just in case. Winnifred knew about the spell, but she didn't memorize the incantation. So she needed the book to see how to cast it.
Phixius ★
If you pause the movie, you will see that the book opened up to the Black Flame Candle spell.