Thanks very much everyone. We're going through the various links.
Just to clarify, she's not necessarily looking to get into designing narrow boats specifically, but she's interested in the fact that people in this area have faced a lot of challenges in efficiently fitting various functions plus storage plus people into a small space, and some of these solutions may be generalizable to other "small-is-beautiful" architecture (whether on land or on the water). This is also primarily about blue-sky / planning ahead ("what might this career look like?"), it will be a few more years until she has to actually choose a program at university.
She is generally avoiding "large-scale" architecture - on her own initiative, but also reflecting my concerns that there can't be as many opportunities to lead projects in those areas. If you want to exercise your creativity in designing small houses, live-aboards, caravans etc there is some opportunity to go out and find a customer. If your dream design is for a stadium, or a mega-yacht, or a skyscraper, your chances of ever getting to build it seem fairly slim just because the budgets to do that are not that common, and will be going to big established design houses. Some of the concepts may be portable, but at that scale I can imagine many of the challenges get beaten into submission with a chequebook...
I probably should not have specified narrow boats in particular - we're here for year from Canada, and they are the design that I associate with the waterways over here, but that's a good point, designers of river-craft in general we could talk to would be of interest!