I don't understand how does a woman or a girl wearing a short dress at a gathering be a problem?

Unless....

- you are a guy and don't want to be caught by your wife staring at the scantily-clad vixens

or

- you are a woman who does not want your husband ogling at those other women ...

Anyways, seriously, I don't know what to say. It's not like ANA is a church or a temple or something. It's not even a business meeting. Most of the people I know who go to ANA go there to have fun and socialize. So unless they show up topless, they should be allowed to wear what they like. If they dress improperly they more often than not find themselves being labeled what they don't like to be labeled as.