Purchase a dog-specific toothbrush from a pet shop, or buy a brush that fits on your finger. You can also opt for gauze on your finger. Buy pet-specific toothpaste; human toothpaste can upset your dog's stomach.
Put some peanut butter, or any food paste your dog enjoys, on your finger. Let your dog lick your fingers while brushing your fingers against her teeth and gums. Repeat twice a day for about three days, then replace the peanut butter with your dog’s toothpaste.
Brush your dog's teeth daily, if possible, and work your way up to longer sessions and to a toothbrush. Hold your dog's muzzle if she struggles.