Dentists who treat young children are faced with challenges. Your daughter is an excellent example of these challenges.
Because she is so young, she may not cooperate with treatment. This means she may not be able to have fillings placed. Also, the teeth in question are very small. They have thin enamel and large nerves. Repairing them requires a very conservative approach with great attention to detail.
However, just because there are challenges with your daughter's situation does not mean that her teeth should not be repaired.
One of the concerns I have is that the decay seems to be getting worse. Also, you seem to lack confidence in the recommendations of your daughter's dentist. I believe that if you have doubts, you should get another opinion from a pediatric dentist.
Pediatric dentists have two additional years of training. They are very familiar with treating young children. You can make an appointment for a consultation and see what the pediatric dentist recommends. After that, you can make a decision about how you want your daughter treated.