"Open day" is a day when the public is allowed to visit a place to which they do not usually have access. The most acurate in Portuguese would be:
dia de (livre) visitação pública
I chose inauguração for being a single word with a very similar meaning.
For all right, the expession means many things, the most likely here is "for sure". I don't think the author was talking about what she looked like, but just stating that he did have seen her.