Start brushing her teeth especially at night.yo may use baby brushes with bristles or silicone bristles. Brush on all surfaces . Get baby toothpaste without fluoride (until she starts spitting) or ask your dentist to recommend one. Else brush without toothpaste until you get one. If she sleeps after feeding,  while here teeth with a sterile gauze wrapped around your finger filled in clean water. Encourage her to eat fibrous foods like apples in bite size pieces. This would naturally keep her teeth clean

You can keep sterile gauze. Wrap it around your fingers. And clean 👶 baby's teeth and gums gently with warm water. Or there are some silicone rubber based finger brushes you can buy on Amazon easily which you can put it on your index finger and then brush baby's  teeth. After few years when spitting habit is more developed in baby very small amount of toothpaste can be put on same brush.