Quote 1
"The first time," Hortensia said, "I poured half a tin of Golden Syrup on to the seat of the chair the Trunchbull was going to sit on at prayers. It was wonderful. When she lowered herself into the chair, there was a loud squelching noise similar to that made by a hippopotamus when lowering its foot into the mud on the banks of the Limpopo River. […]" (10.17)
In this conversation, Hortensia describes a glorious prank she played on the Trunchbull, during school prayers of all times. This is one brave girl. From this quote, we also learn that she's quite well read. How do we know? Well she references Just So Stories (in which there is a Limpopo River). Most likely, the only other people who would know this book are Miss Honey, Mrs. Phelps, and Matilda. And Hortensia doesn't believe Matilda has read it.
"She's mad," Hortensia said.
"But don't the parents complain?" Matilda asked.
"Would yours?" Hortensia asked. "I know mine wouldn't. She treats the mothers and fathers just the same as the children and they're all scared to death of her. I'll be seeing you some time, you two." And with that she sauntered away. (10.65-67)
The Trunchbull keeps getting scarier. She's all the more frightening because powers seem almost unlimited. No adults can stand up to her. It's one thing for children to be afraid of a grown-up. When other adults are afraid of that grown-up, too, you know things are really bad. (Why didn't any of the parents call the police? Or social services?)
Quote 3
"Only yesterday the Trunchbull caught a boy called Julius Rottwinkle eating Liquorice Allsorts during the scripture lesson and she simply picked him up by one arm and flung him clear out of the open classroom window. Our classroom is one floor up and we saw Julius Rottwinkle go sailing out over the garden like a Frisbee and landing with a thump in the middle of the lettuces. […]" (10.42)
It's almost like the Trunchbull is a legend, rather than a person. Hortensia's stories about what the Trunchbull has done to other kids make a terrifying background for the character, and they set up what will happen when the Trunchbull actually enters. Until then, it's almost like she's a mythic monster that the kids tell ghost stories about. Surely her violence can't be that bad.