Did they say what grade hip dysplasia it is? what kind of brace is she going into?
My DD had grade 2 hip dysplasia, we had ultrasounds approx every month -2 months till she was 6 months and she didnt end up needing to go into a brace as she was borderline. By 6 months her hips had corrected themselves. I think it depends on the specialist on how cautious or aggressive the treatment he suggests is, as I know another baby who was in a brace who's hips were the same as my daughters.

Gluck with it all, I know it is scary when anything is "found and needs to be fixed"!