Typically most of these villainess stories have the heroine as some commoner. I'm surprised Louise is a commoner. Rich yes, probably far more rich than Stella, but shes still a commoner. Meanwhile Stella has like noble blood?
Either way I feel bad for original Louise. I don't see how the daughter of a rich commoner could really be able to cause that much damage. Also are they really that rich...they're a flower business..
Anyway these details about why the dress was changed can be found in the novel, which so far the manhwa is following. I think it will be explained soon.