I worked as a pediatric dental assistant before I had my baby and became a stay at home mom. I don't want to offend anyone but the claim that your child's teeth are immune to cavities or won't rot is not true. Brushing (I hate to make it harder but flossing too) teeth right now is so very important because this is the age that they start to realize what is important to YOU and it starts becoming important to them. You would not believe how many small babies and children I saw with tons of cavities! Their parents weren't bad parents either, they just didn't know or they didn't want to make their child unhappy!
Here are some ideas you can try out:
*Have a girl time or princess time: ask if she wants to brush your hair and help you brush your teeth, teach her how to brush YOUR teeth properly, depending on how she reacts tell her you want her to try it with hers.
*Give a play toothbrush and a string of floss (call it fairy hair or princess string) to brush and floss her baby doll's teeth. Allow her to do this without trying to brush or floss her teeth right then unless she asks. Let her just play and practice. Praise her a lot! Praise the doll for being so good too.
*See if just telling her in an excited voice "Let's go brush our teeth now!" BEFORE you get to the bathroom so it is not a surprise.
*Even chewing on a toothbrush several times a day with or without toothpaste will help a lot.
*Talk to her about it like when you are eating lunch or just whenever she is in a good mood and there is no pressure: using simple language like "It makes mommy really sad that we have a hard time brushing teeth." " Your teeth and toothbrush are friends with each other and they like to play, don't you like to play with your friends?" Be creative.
Keep trying. Try to make it a good experience and be in a good mood yourself. Try for at least 10 minutes before you resort to holding her down. Stay calm throught the whole thing. Flossing will take a lot longer and try really hard not to hold her down with flossing because she will bite down on your finger. You can try disposable flossers and see if she likes those. Good Luck.