Your pediatric dentist is probably referring to amelogenesis imperfecta. You may google the entity to get detailed information. In brief, there is nothing we can do other than put a crown if enamel chips away.
I actually work with Sensodyne and they just came out with a new kid's toothpaste(ProNamel for Children) that was developed with dentists to prevent acid erosion and cavities. It has also been scientifically proven to re-strengthen tooth enamel.
You may want to give this a try to see if it can help with your daughters weak enamel. You can get more info and a $1 off coupon at www.ProNamelForChildren.com. Hope this is helpful :)
Did this affect only her baby teeth or permanent teeth too?