It will give everyone a chance to calm down. Then try again in a month or so, but use a reward system to motivate her, not consequences. For children who are looking forward to a visit from the Tooth Fairy, tell them that she's most generous to children who leave properly-cared for, clean, white teeth under their pillows. Use fun, colorful, kid-flavored toothpaste and a toothbrush that is sized appropriately for your child's age. Toothbrushes sizes come in toddler, junior, and up.
Some children are more motivated to brush with an electric toothbrush.
An added bonus is that the electric brushes help time brushing by beeping every thirty seconds. Get some disclosing tablets from your dentist. Have your child chew one after brushing. The tablet will show him which spots he's missing or not brushing long enough. Teens who require lots of dental work due to neglect may be required to help pay for a portion of it.