I agree you have to think outside the box in terms of profession if not going the traditional college route. There are jobs in all the fields you mentioned that don't require a degree or certification, as well as untapped markets for businesses that could grow out of unique skills acquired as an unschooler. Teenage unschoolers often take on volunteer work or internships in fields that interest them, which could lead to low-level positions in a desired field, and could then, if desired, work toward a degree through an online university or working adult program for less cost and wind up a graduate (around the same age as their peers) with extensive actual work experience in the same field as their degree, which would give them an edge in the real world. Starting with the ZTC method at least lets them try before they buy, so to speak.
If your daughter ended up being interested in teaching, she could start with preschoolers, teach English overseas to adults, tutor students of any age online or in person, or become a mentor at a Sudbury, democratic, or free school. Heck, she could even open a free school or learning cooperative if she wanted to. Those are all opportunities she could pursue without a diploma. I'd be willing to bet there are more.
I hope to help my kids avoid the paralyzing fear I have seen other young college students experience as they work their backsides off for a degree in a field they're not even sure they want to go into. Once you've committed to that path, it's hard to escape if you find it's not for you, and I don't think anybody should ever feel trapped in a life they don't love.
As of now, DS wants to be an engineer/designer of some kind. He's 7 so that'll likely change, but it may not. We've discussed how a person might get to that place. Different colleges that cater to that type of career path have come up (he thinks MIT would be awesome, in part because he loves Boston), but we also talk about building skills, networking online and IRL with people already in the field, and keeping a portfolio that showcases your ideas. While there are many jobs, particularly industrial, that would require a degree, I suspect he could get a job with Lego or Henson or somewhere else in a more entertainment-oriented company with enough evidence of ability/determination/charisma. He's got those last two in spades btw, far more than I do. And even if he couldn't, there are a million and one entrepreneurial directions he could take electronics, construction, and programming skills with or without a degree.