It's kind-of Victorian, kind-of not, reminded me somewhat of the costumes in The Young Victoria, and something that I could easily get my hands on without paying ridiculous international shipping fees. It looks kind of like this dress c.1840 that I found on Pinterest:
I'm going to make it out of these delish mauve curtains I found, with trimmings of a purple-shot-with-green taffeta.
I've been putting the project off so far because I wanted to make sure I had the time and resource to do it properly. I imagined doing something Downton Abbey-esque, kind of like these: