A woman in a white wedding dress is being dressed and fitted by two other women.
A woman is being fitted for the first time.
A woman being fitted is not assumed to be doing so for the first time.
Just because  a woman in a white wedding dress is being dressed and fitted by two other women, doesn't mean she is being fitted for the first time.
This may not be the first time this woman is being fitted; she may have tried on another dress before.