No need to worry about tooth decay. They are her first set and important of course, but they will fall out and gorgeous ones will come in at which point brushing will be necessary.
Try this.....does she like music? There are toothbrushes out there(walgreens, Rite aid, walmart, target)that play music as you press the brush to your teeth. First, take her shopping with you, find these toothbrushes and play with them, with her. Make it a big deal, get excited, laugh, giggle, sing along with it and buy it. Get her the yummy toothpaste, bubblegum, bubblemint, whatever flavor, please don't use adult toothpaste because at this tender age, they hate it. It stings. When you get home, don't make a big deal and just put brush in a cup with her name on it. When it comes time to brush, go in with her and prepare her toothbrush and yours. Mommy does it first and then she does it, with that cool brush that plays music. Take turns brushing....mommy, baby, mommy, baby......make it a game for her. Remember, brushing is supposed to be fun, not a chore. So each time, make it fun for her. And if she does well with it, reward her nightly with a story before bed or a puzzle before bed in her bed or songs before bed and she will associate it all with a good time spent with mommy. Good Luck!