Having said that, if everyone is having a long dress I wouldn't like my girl to feel out of place wearing a short dress. However... I wouldn't be happy about it.
DISCLAIMER:
I may have strong feelings about this as a few years ago my now exH and I were asked to be godparents to a girl. We had a good relationship with the girls (they were 2 sisters) and with one of them in particular so it was a bit of a surprise that they asked us to be godparents to the older one and asked another couple they didn't know well to godparent the other.
The buildup for the ceremony was hideous with mother getting so wound up about idiotic things: From the dresses to the cushions the girls were going to kneel on. Passing for the veils, the place of the party afterwards, the thibg to hold the veils, etc.
At some point the mother asked me to do some cards to give to the invitees specifying she wanted a praying, the name of the church, the priest, the city, the country, full double barred names of the 4 goodparents, etc. There was so much info that I ommited the surnames and the city/country details. Mother went ballistic and ordered a new set who she distributed in fron of me, her excuse was that she wanted every one to know that her dds's god parents were well known members of the staff of a prestigious university no matter that our Hs then hardly knew the girls!
We went from one thing to another which included the mother asking me not to bring extra invitees as she didn't want people gatecrashing the party (FGS!can't imagine ANYONE wanting to gatecrash a FC party!). And culminated with her ringing asking what H was going to wear on the day And what is worse all the ridiculous posh parafernalia this woman planned looked totally out of place taking place in a student mass at a classroom in the university.
As you can imagine we are no longer friends with this demented woman, actually, the issue took such importance that we are no longer friends with the other couple either! Our goddaughter let us know that her mother had forbid her to speak to us but I don't care, the only thing I could possibly do to offend this woman is that I decided not to take communion on the day, but then with my head bursting with un christian thoughts, what else could I have done?
Hence, every single sacrament there on, in our family, would enjoy the privilege of being simple, casual, and above all... clandestine