Fact is you both have lessons to learn. You to ensure this is resolved and to ensure your new child does not suffer similarly. She to ensure she suffers no more.
Part of the future is to make yourself aware of what drinks and foods will do damage to your children. When they do have something with sugar in then give them milk or cheese afterwards as these take the PH in the mouth back towards neutral. Water does not do it anywhere near as effectively.
Demonstrate how much you love your childrenYou are in a position to support her by making sure it doesn't happen again. Good luck.